Plush, medium, or firm: how to actually know which mattress is right for you

You’ve been on the Sleepy's website for twenty minutes and “medium” is starting to look mighty appealing. It’s in the middle, after all. And maybe medium is the best choice for you. But when you’re investing in better sleep, “probably close enough” isn’t really the goal. 

A mattress firmness scale describes how a mattress feels, but it doesn’t tell you how that mattress will feel under your body. Soft doesn’t automatically mean comfortable, medium isn’t the universal safe choice, and firm doesn’t always mean better support.

The more useful questions are: what positions do you sleep in, how does the mattress distribute pressure across your body, and can you tell when a surface is too soft or too firm for you?

In this mattress firmness guide, we’ll show you how those three questions give you a much clearer way to understand mattress firmness levels and give you a better place to start.

Why 'medium' isn't a safe default

“Medium” sounds like the sensible middle ground, but mattress firmness isn’t one-size-fits-all. It describes how soft or firm the surface feels, and that feeling changes depending on the person lying on it.

Your sleeping position, body weight and any existing pain all affect how deeply you sink into a mattress and where pressure builds. So the same medium mattress might feel comfortably balanced to one sleeper, too firm through the shoulders to another and too soft through the middle to someone else. That’s why choosing a medium by default can miss the mark. 

Sleep position: what side, back and stomach sleepers each need

Firmness may get the headline, but sleep position is the fine print worth reading first. It shows where your body needs pressure relief, where it needs support and which feels are worth trying. Let’s look at how mattress firmness works when it comes to sleep positions.

So rather than asking, “Am I a medium mattress person?”, ask what your usual sleep position needs the mattress to do. 

Body weight and distribution

Hips, shoulders and midsections all put their own demands on a mattress, which is why one person’s “just right” can be another person’s “not quite”. Body weight changes how deeply you compress the comfort layers and how much support you need underneath. 

• Lighter bodies tend to sink less into the surface, so a mattress can feel firmer than expected. A softer feel may help create better cushioning and pressure relief.

• Heavier bodies usually compress the mattress more deeply, so a firmer feel can help prevent excessive sinking and keep the body better supported.

Same mattress, same label, very different experience. Where your body carries weight changes where the pressure lands.

Existing pain or physical conditions

If you’re already waking up with a cranky back, hip or shoulder, a mattress firmness guide gets even more personal. Where the pain sits and how your body responds to pressure can all change what feels comfortable.

A sore hip or shoulder usually points towards more cushioning around that pressure point. Lower back discomfort often calls for stronger support through the middle, with enough give to keep the surface comfortable rather than rigid.

The useful takeaway: don’t jump straight to “firm”. Match the mattress to the area that needs relief, then check that your body still feels well supported overall.

If pain is ongoing, or severe or getting in the way of daily life, it’s worth chatting to your GP or health professional as well as reassessing your mattress.

Busting the myth: is firmer always better for back pain

“Bad back? Buy a firm mattress” has become one of those beliefs that gets passed around like “wait 30 minutes after eating before you swim”. Familiar, confident, and a little overdue for a fact-check.

Research suggests that medium-firm mattresses can outperform very firm mattresses for back pain, because they can provide support without piling extra pressure onto already sensitive areas.

Too firm and your shoulders, hips or lower back may cope with more pressure than they’d like. Too soft, and your body can sink far enough to make comfortable alignment harder to maintain.

Support versus comfort layers: the distinction most guides miss

Here’s the bit the comfort feel contest tends to leave out: on a spring mattress, support and comfort come from different parts of the bed.

Like shock absorbers for your sleep, the spring system flexes under pressure, then rebounds and redistributes support as you change position. Ideally, your shoulders, hips and midsection can settle at different depths while your spine stays in a more natural line, rather than dipping or being pushed out of shape.

The comfort layers sit above it, usually made from materials like foam, fibres or other cushioning layers. They’re what give you the plush, medium or firm label.

So yes, a mattress can feel soft and still be seriously supportive underneath. And a mattress that feels very firm on top isn’t automatically doing a better job of supporting your body.

Firmness is the first feel. The spring system is the behind-the-scenes crew keeping everything in line.

Bring your answers to a Bed Fit

The goal isn’t to walk into the store knowing exactly which mattress you need. It’s to walk in knowing the right questions to ask. How do I sleep? Where do I need pressure relief? What feels too soft or too firm for my body? That gives your Bed Fit a much better place to start.

The right answer comes from lying on the right mattress with the right guidance. A Sleepy’s sleep expert can help you compare different feels, see how your body responds and narrow things down based on comfort, pressure relief and support.

Use the Find Your Mattress tool and Mattress Buying Guide to get started, then book a bed fit with your local Sleepy’s store and find your amazing.

Frequently asked questions

What mattress firmness is best for back pain?

There is no single best mattress for back pain. Medium-firm often works well for some people with lower back pain because it balances support and pressure relief. The right choice depends on your body, sleep position and where the pain sits.

Is a firm or soft mattress better for side sleepers?

Yes, when it comes to mattress firmness for side sleepers, softer or medium firmness levels tend to be the favourites because they give the shoulders and hips more room to sink in and reduce pressure. Body weight is also a factor, so the best choice is the one that cushions those pressure points without letting the body sink in too far.

What firmness should couples choose?

Couples should look for mattress firmness levels that work best across both bodies and sleep styles. If your preferences differ, try a medium or medium-firm as a starting point, then compare how well it suits each person rather than choosing purely on the ‘safe middle ground’ label.

Does body weight affect which mattress firmness I need?

Yes. Lighter bodies usually compress the comfort layers less, so a mattress can feel firmer. Heavier bodies tend to sink further into the surface and may prefer firmer support.

How do I know if my mattress is too firm or too soft?

Use this mattress firmness guide: if you wake with pressure or numbness around your shoulders and hips, the mattress may be too firm. If your hips sink noticeably lower than the rest of your body or you feel unsupported through the middle, it may be too soft. The right feel should cushion pressure points while keeping your body comfortably aligned.