We reckon side sleepers do best on a medium-soft to medium-firm mattress. The cushioning feel of medium-soft is good for relieving pressure, especially on your shoulders and hips. But if it’s too soft, you’ll sink into the mattress which will strain your spine as it won’t be in its proper position. Hence why medium is probably your sweet spot.If you prefer medium-firm to firm mattresses, which might lack the plush cushioning and pressure relief of softer mattresses, you could opt for a firmer mattress with a cushioned mattress topper.