Kevin,
I am now working through my 4th week post op after having my right hip resurfaced by Dr. Gross and also found it very difficult to sleep flat on my back due to some chronic right side siatica problems. I was also told this pain had probably been caused by my favoring the bad right hip for some time. As did Pat, I also found sleeping with a big pillow between my knees helped, and it allowed me to rotate to my left side (for temporary periods at first) which took some pressure off of my lower back. As the days went by I was also eventually able to sleep a little on that left side and also lay on my stomach some around the end of the second week. Any position seemed to be better than laying flat on my back.
Also during the first week or so after my surgery I benefited from a large sofa cushion placed underneath both of my lower legs at the foot of the bed. This not only elevated my legs to keep the swelling down around the incision but took the pressure off of my lower back. Lee Webb, RNP, Dr. Gross's assistant, suggested this to "keep my toes above my nose" as she put it. It works.
One other thing; I purchased a Zero Gravity Chair and had it placed in front of the big screen in the den to lounge and sleep during the first couple of weeks. I still use it today to get my legs to heart level and to take the pressure from my lower back. I found these chairs in the Cabela's catalog as Chaise Lounger chairs but you may be able to purchase one locally as well. To me, the chair has made my recovery much more tolerable.
By the way... It gets much better very fast! I'm sleeping in any position with reasonable comfort now other than directly on that right side now at 4 1/2 weeks. I believe the PT (including walking, walking, walking) is the key along with the normal healing process.
Good luck Kevin.