Leg Elevation Pillows
Raising the legs is easy for ten minutes and hard for eight hours, because a stack of ordinary pillows slides out from under you as soon as you move. A molded wedge holds one angle whatever you do on top of it.
Look at the surface as much as the shape. Legs resting on foam for a full night get warm, so a cooling or breathable cover is the difference between using it and kicking it off. Some versions here are contoured with channels for each leg, which stops them rolling together.
If the goal is keeping the hips square rather than raising the legs, knee pillows sit between them instead. For a general incline, see wedge pillows.