Knee Pillows

Side sleeping lets the upper leg drop forward, which rotates the pelvis and pulls on the lower back all night. A pillow between the knees keeps the legs stacked so the hips stay square.

The contoured hourglass shape is doing real work: the waist in the middle grips between the knees so it travels with you when you turn, instead of being left behind on the mattress the first time you move. That is the single thing that separates a knee pillow you keep using from one that ends up on the floor.

For full length support rather than just the knees, see body pillows. To raise the legs entirely, leg elevation pillows hold a fixed angle.