For side sleepers who want a firm mattress the best mattress firmness that is best for side sleepers is a medium firm to medium mattress firmness.
Side sleepers should actually avoid a firm mattress though.
It simply does not provide the right amount of give for this sleeper.
Think about laying on hardwood floors on your side, it's not comfortable because you feel pressure against your shoulder and hip.
A side sleeper should use a medium-soft to medium-firm mattress.
Side sleepers should watch out for hip and shoulder pain and a medium-soft to medium-firm mattress can give the correct support while gently cradling the hips and shoulders to prevent stress and injury.
In general, a medium-firm mattress is ideal for side sleepers, as it allows for spinal support, but it is flexible to adjust to the body curvature, adding that those who weigh more will see greater benefits by opting for a firmer mattress.
When sleeping on your side, try placing a pillow between your knees to help with spine alignment.
Use a thicker pillow if sleeping on your side and a thinner pillow when sleeping on your back.
If sleeping on your stomach, try putting a pillow under your pelvis and consider using a thinner pillow under your head.