How Firm Should Your Mattress Be? Soft, Medium or Firm

Key takeaways

• Mattress firmness is about how hard or soft a bed feels on the surface, but good comfort also depends on support from the layers underneath.
• Your body weight and shape strongly influence what feels right: lighter people usually prefer softer feels, while heavier sleepers often need medium-firm to firm support.
• Side sleepers tend to do better on soft to medium mattresses; back and stomach sleepers generally need medium to firm to keep the spine aligned.
• If you wake up with a stiff lower back, your mattress may be too soft; sharp pressure on your shoulders or hips can mean it is too firm.
• For children, a supportive but not overly hard mattress such as the Silentnight Kids Snooze Eco Mattress can provide balanced comfort as they grow.

What is mattress firmness?

Mattress firmness describes how hard or soft a bed feels when you first lie down. It is about your initial comfort, not the deep support structure inside the mattress. When brands talk about soft, medium or firm, they are usually describing the feel of the upper comfort layers that your body interacts with most.

Many manufacturers use a numerical firmness scale, often from 1 to 10. While there is no universal standard, you can think of it roughly like this:

• Soft: 3–4 out of 10
• Medium-soft to medium: 5–6 out of 10
• Medium-firm to firm: 7–8 out of 10

Numbers can help, but they are not everything. Two mattresses both labelled ‘medium’ can feel quite different depending on whether they are made from memory foam, springs, or a hybrid of both. That is why it is useful to understand firmness in relation to your body weight and sleeping position, not just marketing labels.

Firmness vs support: what is the difference?

Firmness and support often get mixed up, but they are not the same thing. Firmness is the surface feel; support is how well the mattress keeps your spine in a healthy, neutral line. You can have a soft-feeling mattress that still offers strong support underneath, and you can also have a very firm mattress that does not actually support your curves properly.

Imagine lying on a soft cloud that sinks too far in the middle: it feels plush, but your hips drop and your lower back arches. That mattress is soft and unsupportive. Now imagine a very firm board: it keeps everything flat, but there is no cushioning at your shoulders and hips, so pressure builds up. That mattress is firm but not comfortable. The goal is to combine the right level of surface softness with deep support that matches your body.

Good support usually comes from the core of the mattress: the coils in a sprung bed or the denser base foam in an all-foam design. The comfort layers on top add cushioning and adjust the feel, whether that is soft, medium or firm. When you are choosing firmness, you are really deciding how much you want to sink into those upper layers before the support underneath “catches” you.

How body weight affects ideal firmness

Your body weight and overall build play a big role in how a mattress feels. The same mattress can feel soft to one person and firm to another, purely because of how far each person sinks into the surface.

As a general guideline:

• Lighter sleepers (under roughly 9–10 stone / 60–65 kg) often find medium or even firm mattresses feel harder than advertised. They do not sink as far into the comfort layers, so a medium mattress can feel closer to medium-firm. Many in this group are more comfortable on soft to medium feels.
• Average-weight sleepers (around 10–15 stone / 65–95 kg) are usually the target for most “medium” mattresses. A medium or medium-firm bed often gives a good balance of cushioning and support.
• Heavier sleepers (over roughly 15 stone / 95 kg) tend to sink deeper into the comfort layers. A soft mattress may bottom out and feel unsupportive, which is why medium-firm to firm options usually provide better spinal alignment and durability.

Build matters too: someone with broader shoulders, pronounced hips or a curvier figure applies pressure in concentrated areas, which can make firmer beds feel harsher. Slighter, more evenly built people spread their weight more evenly, so they might find a firmer mattress acceptable.

How your sleep position changes what you need

Your favourite sleep position is just as important as your weight. Different positions put different parts of your body under pressure, and your mattress has to accommodate those curves while still holding your spine reasonably straight.

Side sleepers

Side sleepers need enough cushioning for their shoulders and hips to sink in slightly, otherwise these pressure points can become sore. For most side sleepers:

• Lighter side sleepers often prefer soft to medium-soft.
• Average-weight side sleepers usually do well on medium.
• Heavier side sleepers may need medium to medium-firm so they do not sink in too far.

If you wake with numb arms, tingling hands or sore hips, your mattress may be too firm for side sleeping. A mattress that gently hugs your curves without letting your midsection dip too deeply is ideal.

Back sleepers

Back sleepers need the mattress to support the natural curve of the spine without letting the hips sink too low. Too soft and your lower back can arch; too firm and there is not enough contouring at the small of your back.

Most back sleepers are comfortable on medium to medium-firm mattresses. Lighter back sleepers might enjoy a slightly softer medium, while heavier back sleepers tend to benefit from medium-firm or firm support. If you often wake up with a stiff lower back, it can be a sign that your mattress is too soft for back sleeping.

Stomach sleepers

Stomach sleeping places extra stress on the neck and lower back because your head is usually turned to one side and your middle can sink more than the rest of your body. A mattress that is too soft can allow your hips and stomach to dip, putting strain on the spine.

For this reason, stomach sleepers usually do best on medium-firm to firm mattresses, especially if they are average or heavier in weight. Lighter stomach sleepers can sometimes get by with a supportive medium mattress, but very soft beds are generally not recommended for this position.

Combination sleepers

If you move around a lot at night, you need a compromise that works reasonably well in all positions. A medium or medium-firm mattress often hits the sweet spot here, offering enough cushioning for side sleeping while keeping sufficient support for back and stomach positions.

Responsiveness matters too. Beds that are very slow to respond to movement can make turning over feel like an effort. If you switch positions regularly, a slightly firmer, more responsive surface can make the mattress feel easier to move on.

Back pain, posture and spinal support

If you experience back pain, firmness choice becomes even more important. While there is no single perfect firmness for everyone with a sore back, research and clinical experience generally suggest that extremely soft or extremely hard mattresses are less likely to be comfortable long-term.

For many people with back issues, a medium-firm mattress provides the best blend of comfort and support. It usually keeps the spine closer to neutral alignment and limits excessive sinking, while still providing some cushioning. However, your weight and sleep position can tilt this slightly softer or firmer.

When considering back pain, pay attention to where the mattress supports or fails you:

• Lower back pain on waking: often linked to a mattress that is too soft or sagging in the middle.
• Sharp pressure or discomfort in the hips or shoulders: can be a sign your mattress is too firm, especially if you are a side sleeper.
• Mid-back stiffness: sometimes appears when a mattress is extremely firm and does not allow your natural curves to sink in at all.

If back support is a priority, it can also be useful to learn about different constructions. For instance, some people find that memory foam and hybrid mattresses contour more closely around painful areas, while others prefer the firmer, buoyant feel of traditional spring beds. Our guide to the best mattresses for back pain and spinal support explores this in more detail.

Comfort is personal, but spinal alignment is universal. Whatever firmness you choose, your mattress should let your spine rest in a neutral, natural line without noticeable sagging or arching.

Simple self-assessment checks

If you are not sure whether your current mattress is too soft, too firm or about right, a few simple checks can help. These are not medical tests, but they give you practical clues about how well your bed is working for you.

• Lie on your back and slide a hand under your lower back. If you can push your hand through a big gap with little resistance, your mattress may be too firm. If you cannot get your hand in at all and you feel your lower back sagging, it may be too soft.
• Check your side profile in a mirror or with a photo. When lying on your side, your spine should look fairly straight from neck to tailbone. If your hips sag down or your shoulder is jammed up towards your ear, your mattress firmness might be off.
• Notice morning symptoms. Consistent stiffness that eases as you move around may suggest your mattress is not supporting you correctly. Focus on where you feel it most: shoulders, hips, lower back or neck.
• Think about how you move at night. If you wake often because you are turning to find a comfortable spot, your current firmness (or an aged mattress) may not be suiting you.

Use these observations alongside your body weight and sleep position to guide your choice, rather than relying purely on mattress labels.

Soft, medium or firm: who each suits best

While there is no rigid rulebook, you can use the following broad guidelines when considering soft, medium or firm mattresses.

Who soft mattresses suit

Soft mattresses tend to suit:

• Lighter adults who sleep mostly on their side.
• People with prominent shoulders or hips who find firmer beds too sharp.
• Those who like a “hugged” or deeply cushioned feeling.

Soft beds are not usually ideal for heavier sleepers, dedicated stomach sleepers, or people needing strong lower-back support, because they can allow too much sinking in the middle.

Who medium mattresses suit

Medium mattresses are the most popular for a reason: they offer a workable balance for a wide range of people. They often suit:

• Average-weight side sleepers who want cushioning without wobbliness.
• Back sleepers who like a little give but good overall support.
• Combination sleepers who change position through the night.
• Couples with slightly different preferences who need a compromise.

If you are unsure where to start and you are around average weight with no specific problems, a true medium or a medium leaning slightly firm is often a sensible starting point.

Who firm mattresses suit

Firmer mattresses usually suit:

• Heavier sleepers who need stronger support to avoid sinking too deeply.
• Stomach and many back sleepers who want their hips kept level with their shoulders.
• People who prefer to lie “on” the bed rather than “in” it.

Firm does not have to mean uncomfortable: a good firm mattress should still have some cushioning in the top layers. However, very light side sleepers and those with sensitive shoulders or hips can find firm beds too unyielding.

Mattress firmness for children

Children’s needs differ slightly from adults. They are lighter, constantly growing and often sleep in a mix of positions. Young children in particular do not generally need very soft mattresses; a supportive, medium-feel bed is usually better.

A good example of a balanced children’s mattress is the Silentnight Kids Snooze Eco Mattress. It combines a traditional Bonnell spring unit with cushioning and breathable eco-fibres to provide gentle support rather than a hard board-like feel. For many children, this kind of medium-support mattress helps keep growing spines aligned while still feeling comfortable.

Some parents choose memory foam for contouring comfort. A design like a kids’ memory foam mattress with orthopaedic support can offer gentle pressure relief with a medium feel, helping to keep joints comfortable at night. Always check that children’s mattresses are supportive, appropriately sized and meet safety standards.

Practical tips for choosing the right firmness

Once you have a rough idea of the firmness you need based on weight and position, a few practical strategies can help you refine your choice.

• Be honest about your main sleep position. Choose firmness for the position you spend most of the night in, not just the position you fall asleep in.
• Consider your partner. If you share a bed and have different needs, a medium or medium-firm mattress is often a good compromise. Some couples use a mattress topper on one side to soften it slightly.
• Account for your pillow and base. A very high or low pillow can change your neck alignment, and a rigid or flexible base can alter how firm the mattress feels overall.
• Think long-term, not just first impressions. Extremely soft mattresses can feel luxurious for short tests, but day-to-day support matters more over time.
• Allow a short adjustment period. When you change firmness significantly, your body may need several nights to adapt. Mild initial discomfort does not always mean the mattress is wrong, but persistent pain is a red flag.

Signs your current mattress firmness is wrong

If you are trying to decide whether to replace your mattress or perhaps adjust it with a topper, look out for these firmness-related clues:

• You wake most mornings with new or worsening back, neck or hip pain that eases as the day goes on.
• You can see obvious dips, sagging or raised areas in the mattress surface.
• You often roll into a “valley” in the middle of the bed, or towards your partner.
• Your shoulders or hips feel uncomfortably jammed or numb, especially when side sleeping.
• You feel like you are fighting the mattress to get comfortable or to move around.

In some cases, a good-quality mattress topper can tweak the feel of an otherwise supportive but too-firm bed, adding softness for pressure relief. If you are interested in alternatives such as toppers, futons or sofa beds for occasional use, our guide to mattress alternatives explores how they compare.

Special situations and firmness

There are a few situations where firmness choice may need extra thought:

• Very light adults or teenagers: Firm mattresses can feel uncomfortably hard because they do not sink in enough. A soft to medium mattress is often more suitable.
• Very tall or heavier sleepers: They typically need medium-firm to firm support, possibly with thicker comfort layers to avoid “bottoming out”.
• People who overheat: Softer memory foams can sometimes trap more heat. If you prefer softer feels but tend to get warm, look for breathable, cooling designs or consider the options in our guide on how to sleep cooler on a mattress.
• Guest beds and sleepovers: For occasional use, flexible solutions like a kids’ inflatable airbed and sleeping bag in one can provide a reasonably supportive surface without committing to a permanent mattress.

Conclusion

Choosing how firm your mattress should be is all about matching your body weight, sleep position and comfort preferences to the right level of cushioning and support. Instead of thinking in rigid categories, use soft, medium and firm as starting points and refine from there using simple self-checks and your own morning comfort as a guide.

Remember that the best firmness for you is the one that keeps your spine in a neutral position, avoids pressure points at your shoulders and hips, and allows you to wake feeling rested rather than stiff. For children, a supportive but not overly hard mattress such as the Silentnight Kids Snooze Eco Mattress or a well-designed kids’ memory foam mattress will usually provide a healthy balance.

If you are still unsure after considering the guidance in this article, you can use broader buying advice covering size, materials and budget to narrow down specific models that match your preferred firmness and sleeping style.