‘My advice would be to avoid' – sleep experts warn this is the one type of mattress you shouldn't buy

There's a lot to think about when buying a mattress. Memory foam or hybrid, with a sleep trial or without, all can have an impact on how well you sleep on your new bed.

But if you want to avoid any costly mattress buying mistakes, experts warn that there is one type of mattress you should never buy.

What is it? A mattress that's under 20cm deep. At least if you're an adult, and not a child. I enlisted the help of two sleep experts to explain why.

In the hunt for the best mattress money can buy, you might be wondering if mattress depth matters, and the answer is yes.

A typical mattress thickness ranges from 20cm to 30cm. The best budget mattresses will all tend to err on the thinner side. After all, less mattress depth means fewer materials are needed, so it stands to reason a thinner mattress will cost less.

In contrast, a luxury mattress tends to sit somewhere between 25cm and 35cm deep. That extra depth usually houses taller, more robust springs and more comfort layers that can add up to a more supportive and better cushioned sleep.

If you're looking for an affordable mattress, that means you're likely to be investing in a thinner mattress, but sleep experts say there is a mattress depth that you shouldn't ever go below if you want a comfortable sleep. If you're buying a mattress for an adult, that's any depth mattress below 20cm.

‘My advice would be to avoid mattresses any thinner than 20cm as they tend to have insufficient support,' warns Chris Tattersall, sleep expert and managing director of bedding brand Woolroom.

'In a mattress of this depth the springs can be too short, and can only take a certain amount of weight or use before the comfort layers begin to compress down into the base.’

‘A 20cm mattress can be sufficient for lighter individuals, children, or occasional use (like in guest rooms),’ agrees Martin Seeley, sleep expert at mattress retailer MattressNextDay. ‘But for everyday adult use, especially if you have a heavier build or joint issues, a mattress of a 20cm depth or lower may not offer enough depth for proper spinal alignment or durability over time.’

'I would generally consider anything under 20cm to be a back-up option,' says Martin, 'it may not last as long or perform as well in regular use.’

At Ideal Home, we've put three mattresses that are 20cm or under through our mattress testing process. The Simba Hybrid Essential Mattress, the REM-Fit Hybrid Pocket 1000 Mattress, and the Zinus Green Tea Memory Foam Mattress. We also tested the 18cm Dreams Workshop Follows Traditional Spring Mattress.

Our tester, Rachel, was impressed by both the Simba and REM-Fit mattresses, considering their price. However, she found the expert's concerns rang true with all the mattresses of this thickness; they lacked support compared to deeper designs.

Overall, the best budget mattress we've tested has been the 25cm deep DreamCloud Hybrid Mattress and the 23cm deep OTTY Aura Hybrid mattress.

Best budget mattresses over 20cm

The main reason you'd be considering shopping for an under 20cm deep mattress is price. These are three budget-friendly alternatives that offer more depth, which equals more support and better durability.

All in all, I think it's clear that it's well worth shopping for a mattress that's over 20cm deep. That means making sure to check the small print if you're buying a mattress online, as depth is something that isn't always apparent if you're not testing a mattress in a store.

Yes, this will often mean you need to invest a few hundred more pounds, but this is where mattress deals can help, as retailers often reduce prices considerably during key sales periods.

Opting for a super cheap mattress that's under 20cm deep is also likely to be a false economy. As our experts point out, there's more likelihood that a thin mattress will become compressed quickly, and that means the mattress will need replacing more frequently than it would otherwise.

Avoid this one mattress-buying pitfall, and you should score yourself a much more comfortable sleep.