MrsJamJam
When I had my hip replacement, two years ago, surgeon said no need to sleep on your back that's old advice, just sleep in any way that's comfortable. The best thing was instantly getting rid of that nagging pain that all OA sufferers will know only too well.
Same here MrsJamJam. I found a fairly flat cushion did the job for me. It is only about 2 or 3 inches thick but was enough to relieve the pain prior to the op.