But again - whether you sleep on your back or on your side, you want your head straight to your spine. Your head should not sink down towards the mattress or be pushed up towards the ceiling. A big mistake many people make, when they sleep on their back, is that they have too many pillows under their head, which pushes their head beyond their shoulders. Unless your mattress has lumps or sags, it is not the mattress. Usually when people wake up feeling like they've been run over by a truck, it is because of the position they sleep in.
Yoga can be wonderful to relieving stress and increasing flexibility.
This will take lots of pressure off your lower back when sleeping. The best positions to sleep in are on your back - especially if you tend to have rounded shoulders. Make sure you do not have too many pillows under your head and do place a pillow under your knees. Sleeping on your side can be fine too. Make sure your head is level with your spine and place a regular size bed pillow between your lower legs.