Most people choose a mattress by what's inside it, but the better starting point is how you sleep. Side sleepers need a softer surface so the shoulder and hip can sink in, back sleepers need their lower back held up, and front sleepers need firmness to stop the hips dropping. This guide covers each position in turn, how your weight and your base change the way a mattress feels, and what to try before you replace one that's giving you trouble.