How Firm Should a Mattress Be? Soft, Medium and Firm Compared

Key takeaways

• Mattress firmness is about how hard or soft the surface feels, not how supportive it is – a soft mattress can still be supportive if it keeps your spine aligned.
• Light sleepers often prefer softer to medium mattresses, average-weight sleepers tend to suit medium to medium-firm, and heavier sleepers usually need medium-firm to firm for proper support.
• Side sleepers usually do best with soft to medium, back sleepers with medium to medium-firm, and stomach sleepers with medium-firm to firm to prevent the hips dipping too far.
• If you want a mattress that balances cushioning and support, a medium-feel memory foam model such as this single memory foam mattress with pressure relief can be a good benchmark for the feel of a 'true medium'.
• Signs your mattress firmness is wrong include waking with new aches, numb shoulders or hips, or a hammock-like dip under your lower back or stomach.

What is mattress firmness, really?

Mattress firmness describes how hard or soft the surface feels when you lie on it. It is about your comfort impression – do you feel like you are lying 'on' the bed or sinking 'into' it? – rather than the internal build quality.

Support, by contrast, is about whether the mattress keeps your spine in a neutral, straight line (or its natural S-curve) while you sleep. A supportive mattress stops your hips, shoulders and lower back from sagging or being pushed out of alignment.

This means a mattress can be soft yet supportive if it gently allows your wider areas to sink in while still holding your spine level. Conversely, a firm mattress can be unsupportive if it is so hard that your shoulders and hips cannot sink in, causing your spine to bend.

Most brands use a 1–10 firmness scale as a rough guide:

• 1–2: Extra soft / plush
• 3–4: Soft
• 5–6: Medium
• 7–8: Firm
• 9–10: Extra firm

However, there is no universal standard, so one brand's '6' may feel like another brand's '7'. That is why it helps to think in terms of soft / medium / firm as broad bands, then narrow down based on your body and sleep style.

Soft vs medium vs firm mattresses compared

To visualise firmness, it can help to imagine a simple scale from 1 to 10:

• Soft: around 3–4
• Medium: around 5–6
• Firm: around 7–8

Here is how each category typically feels and who it tends to suit.

Soft mattresses

Soft mattresses have a deep, cushioned feel where you sink in more noticeably. They are often associated with plush memory foam or thick pillow-tops. Pressure-sensitive areas such as shoulders and hips are cradled, which can feel very comfortable if you sleep on your side or have bony joints.

The downside is that if you are heavier or sleep on your back or stomach, a soft bed can let your hips and torso dip too far, leading to a curved spine. Over time that can contribute to lower back discomfort, especially if the core of the mattress is not firm enough.

Soft mattresses can work well if you are light, primarily sleep on your side, or like a 'hugged' feeling rather than a floating one.

Medium mattresses

Medium mattresses aim to balance cushioning and support. You usually sink in slightly, enough to relieve pressure, but still feel that your body is held up rather than swallowed. This feel often suits couples with different preferences because it sits in the middle ground.

A typical medium-feel memory foam option, such as a single medium memory foam mattress designed for pressure relief, illustrates this compromise: enough contouring for side sleepers, but with a denser core that can still support back sleepers of average build.

Medium is often recommended as a safe starting point if you are not sure what you prefer, especially if you are of average weight and change positions during the night.

Firm mattresses

Firm mattresses have less sink and a more stable, 'on top' feeling. When you lie down, you are supported near the surface and your body does not drop deeply into the layers. This can help keep heavier bodies in better alignment and reduce the chance of feeling stuck in the mattress when you turn.

For people who sleep on their back or stomach, a properly firm mattress can prevent the hips from dipping too far, which is important for lower back support. However, if you are light or have sensitive joints, a firm mattress can feel unforgiving around your shoulders and hips, sometimes leading to pins and needles or soreness.

Firm is usually best for heavier sleepers, stomach sleepers and some back sleepers, especially when paired with comfort layers that provide at least some cushioning over a supportive core.

Think of firmness as your comfort preference and support as the underlying engineering. Your goal is the softest surface you find comfortable that still keeps your spine aligned.

How your body weight affects the ideal firmness

Your weight has a major impact on how firm a mattress feels. A mattress does not change; your body's interaction with it does. Someone weighing 60 kg may describe a model as 'firm' while someone at 100 kg finds it comfortably medium.

As a simple guide:

• Lighter sleepers (roughly under 60–65 kg): Often prefer softer to medium mattresses. Their bodies do not compress the layers as much, so a firm mattress can feel very hard and may not allow the shoulders and hips to sink enough.
• Average-weight sleepers (roughly 65–95 kg): Usually fall in the medium to medium-firm range. They compress the comfort layers more, so a 'medium' design can feel supportive without being too hard.
• Heavier sleepers (roughly over 95–100 kg): Typically need medium-firm to firm. Softer mattresses can allow excessive sink, especially at the hips, which can bend the spine out of alignment.

Mattress construction also matters. A hybrid mattress with coils and foam may feel more supportive for a heavier sleeper even at the same labelled firmness. For example, a medium-firm hybrid mattress with orthopaedic support will usually feel sturdier under a heavier body than a simple soft foam mattress of the same thickness.

Best firmness by sleep position

Your main sleep position is the other crucial part of the puzzle. Different positions load your spine and joints in different ways, so they benefit from different levels of cushioning and support.

Side sleepers

When you sleep on your side, your shoulders and hips bear more of your weight. A mattress that is too firm can create pressure points, leading to numb arms or sore hips. Too soft, and your spine may bend sideways if your waist is not supported.

As a rule of thumb:

• Lighter side sleepers: Soft to soft-medium
• Average-weight side sleepers: Soft-medium to medium
• Heavier side sleepers: Medium to medium-firm with good cushioning on top

Memory foam and hybrids are often popular with side sleepers because of their pressure-relieving top layers. A soft-feel spring-and-foam design like a soft feel single sprung and foam mattress is a typical example of a bed aimed at providing more give for this group.

Back sleepers

Back sleepers need a balance: enough surface softness so that the hips and shoulders can settle, but enough underlying support so that the pelvis does not sink more deeply than the upper back. When the pelvis drops, the lower back arches and can become strained.

General guidance:

• Lighter back sleepers: Medium-soft to medium
• Average-weight back sleepers: Medium to medium-firm
• Heavier back sleepers: Medium-firm to firm

Many people who sleep on their back find a 'true medium' or 'medium-firm' ideal, often in a hybrid or denser foam construction that supports the lumbar region.

Stomach sleepers

Sleeping on your stomach is the most demanding position for your spine because gravity pulls your midsection down. If your mattress is too soft, your hips sink and your lower back curves steeply, which can lead to discomfort.

So stomach sleepers generally need a firmer feel:

• Lighter stomach sleepers: Medium-firm
• Average-weight stomach sleepers: Medium-firm to firm
• Heavier stomach sleepers: Firm, often with a supportive coil or dense foam core

If you cannot change position, focus on finding a mattress that keeps your hips in line with your shoulders and consider a low pillow to reduce neck strain.

Is a firm mattress better for your back?

It is a common belief that a very firm mattress is best for back pain, but the reality is more nuanced. What matters most is spinal alignment and pressure relief, not maximum hardness.

Research and clinical experience often point towards a medium-firm mattress being a good middle ground for many people with non-specific lower back discomfort. Medium-firm tends to provide enough support to prevent sagging while still being forgiving around the joints.

However, the right choice depends on your:

• Body weight – heavier bodies may need firmer than medium-firm, lighter bodies might need something slightly softer.
• Sleep position – side sleepers with back issues often do best where the upper layers are softer but the core is supportive.
• Specific condition – for example, someone with spinal stenosis might need different cushioning than someone with muscle-related tension.

If back pain is your main concern, it can be worth reading a dedicated guide such as how to choose a mattress for back pain relief, and speaking with a health professional if your symptoms are severe or persistent.

A mattress that is too firm can be just as unhelpful for your back as one that is too soft. The right feel is the one that keeps your spine neutral and lets your muscles relax.

Can a mattress be too soft?

Yes. A mattress that is too soft for your body and sleep style can lead to several issues:

• Spinal misalignment: Your hips and midsection may sink more than your shoulders, especially when you sleep on your back or stomach.
• Muscle tension: Your back muscles work overtime to stabilise your spine during the night instead of relaxing.
• Difficulty moving: Deep sinkage can make it harder to roll over, which may disturb your sleep.
• Overheating: Some very soft foams wrap closely around the body, which can trap more heat.

Signs that your mattress may be too soft include waking up with lower back ache, feeling as if you are in a hammock rather than on a flat surface, or noticing a significant body imprint that does not bounce back quickly.

Can a mattress be too firm?

A mattress can also be too firm. When the surface does not allow your shoulders and hips to sink enough, your spine can bend, and pressure can build up around bony areas. This is especially noticeable for side sleepers and lighter individuals.

Common signs of a mattress that is too firm include:

• Numb or tingly arms and shoulders, particularly when side sleeping
• Sore hips or outer thighs after lying on your side for a while
• Feeling like you are lying on a board rather than 'in' the bed
• Difficulty getting comfortable and needing to shift position often

If your mattress is generally supportive but feels uncomfortably hard, you may not need to replace it immediately. A quality mattress topper can soften the surface while the underlying support stays the same.

What if your mattress feels too hard or too soft?

Mattress firmness is not entirely fixed. There are several ways to tweak how your bed feels if you are close to the right firmness but not quite there.

If it feels too firm:

• Add a soft or medium mattress topper, especially one with memory foam or latex for extra cushioning.
• Check your bed base – a very rigid base can make any mattress feel harder; sprung slats may add a little give.
• Allow a break-in period. Many mattresses soften slightly over the first few weeks as the materials settle.

If it feels too soft:

• Ensure your base or frame is sturdy and not sagging in the middle.
• Rotate the mattress regularly, if the manufacturer recommends it, to even out wear.
• Consider a firmer mattress topper that adds a more supportive feel to the surface.

If your mattress is old, visibly sagging, or you consistently wake with new aches despite experimenting with toppers and bases, it may be time to consider a replacement. Exploring options across a range of firmness levels, such as memory foam, spring and hybrid designs, can help you narrow down what truly suits you.

How to choose the right firmness step by step

Putting everything together, you can work through a simple process to decide which firmness is most likely to work for you:

1. Identify your dominant sleep position. If you split your time fairly evenly, pick the position you use most or consider a compromise such as medium.
2. Note your approximate weight range. Use the light / average / heavy guidelines above to see which firmness range you fall into.
3. Consider any pain or sensitivity. If you have back discomfort, joint tenderness or conditions affecting your spine, prioritise alignment and cushioning where you need it most.
4. Think about your current mattress. Is it too hard, too soft, or pretty close? Use that as a reference for moving slightly softer or firmer.
5. Shortlist constructions that suit you. Foam, hybrid and spring mattresses all behave slightly differently; you can explore the pros and cons in more depth in guides such as memory foam vs spring mattresses or hybrid vs foam mattresses.

Once you have a target firmness and type, it becomes easier to filter options and compare models. Reading user reviews from people who share your weight and sleep position can also help translate the advertised firmness into real-world experience.