Pillows are supposed to help keep your spine in a neutral position, align your neck with the rest of your body, and support good posture.
The best pillow for side sleepers is one that’s slightly thicker and firmer for optimal support.
The best pillow for back sleepers is one that’s on the thinner to medium-thick side.
The best pillow for stomach sleepers is one that’s soft and thin. Or, you can go without a pillow.