Seeking mattress experts, physiotherapists, chiropractors, orthopedic specialists and sleep science experts to comment on mattress recommendations for back pain. Please answer these questions: 1. What causes back pain while sleeping? 2. What type of mattress is best for back pain (material, firmness level, etc.)? 3. How do you know if your mattress is causing back pain? 4. Best mattress type by sleeping position?