If you have back pain, maintaining the normal curves of your spine is very important. If your mattress is overly soft, it’s time to get a new one.
Sleeping on your back is probably the best position for you. Place a pillow under your knees to help restore natural spinal curves and reduce the tension in your tendons. You might also try a small rolled towel under your lower back for additional support. If you’re a stomach sleeper, put a pillow under your lower abdomen and pelvis so that the small of your back doesn’t move forward.
If you like sleeping on your side, then it’s best to take the fetal position. Draw your legs up slightly toward your chest, keeping your back naturally arched. Put a small pillow between your knees. This can help you take the load off your lower back.