Firm mattresses are often recommended for bad backs, but those ‘orthopaedic’ surfaces can also trigger new aches and pains.

A firm mattress could give you backache if you weigh less than 200 lbs because it won’t compress enough to put your spine into a natural position – you’ll lay on top of the mattress, with that lack of sinkage misaligning your back.  

Another scenario in which a firm mattress could cause backache is if you are a side sleeper because the firm surface offers no pressure relief.

We provide more information below.

Signs your mattress is giving you a bad back

There are two signs to watch out for:

• You wake up with a lower backache (or some other backache). However, this may also be from a strain or injury the day before.
• You go to bed fine but get a backache after lying there for a while. This is the most significant sign that your mattress is too firm.

If you prefer sleeping on a firm mattress, then more power to you. But most people who sleep on too firm a mattress will have back problems. We know because we have seen it countless times before.

The problem with firm mattresses

There isn’t anything inherently wrong with a firm mattress – some people prefer the unforgiving surface and hate anything squashy.

However, if you have a backache after sleeping and your mattress is firm, it could be to blame, and you might need to change it.

Firm mattresses are best for:

• Front sleepers. If you sleep on your front, you need a firm mattress to support your stomach and eliminate the need for a pillow.
• People with physical deformities need a firm surface to maintain spinal alignment and prevent joint deformities.
• People and couples over 220 lbs because the extra-firm surface won’t collapse under the relatively large weight.

Unless you match the criteria above, a firm mattress probably isn’t the best choice for you.

The best mattress firmness for you

Comfort is subjective—some people love a rock-hard mattress, while others like to sink straight into it and feel ‘stuck.’

However, what isn’t subjective is support, which you need to maintain proper spinal alignment and ensure sleeping doesn’t cause or worsen your back problems.

Here are some recommendations for support:

Body weight

Your body weight is a valuable metric for choosing a mattress based on firmness because it dictates how soft or firm a mattress feels:

• 140 – 180 lbs: A medium mattress is usually best
• 180 – 210 lbs: A medium-firm mattress is perfect
• Over 200 lbs: A firm mattress is best in most cases

You can also get soft-medium mattresses, which are too soft to provide support but offer a squashy, cloud-like sleep surface.

Sleep position

Your favourite sleep position is another helpful indicator for the best mattress firmness because sleeping on your back, front, and side puts different pressure levels on the surface:

• Side sleepers do best with a squashy mattress, usually medium
• Back sleepers do best with a firm but compliant surface, usually medium-firm
• Front sleepers need a firm surface

If you are a combination sleeper, choose a medium-firm or medium mattress based on the body weight guide above.

Summing up

Too firm a mattress can cause bad back pain if it increases pressure on your back or creates an unnatural spine position while you sleep.

The most significant sign that your mattress is too firm is if you go to bed without back pain but get backache after lying there for a while. However, if your mattress has a medium or medium-firm rating, it could be too soft rather than too firm.