Ok. Gone through 3-4 different mattresses over the past 8 years. Non tempurpedic always built gullys on both sides. Had last tempurpedic mattress replaced 6 months ago because it seemed to have a ridge or spine in middle. Now this tempurpedic seems to do the same. Rooms to go is coming out to evaluate next week. What mattress should we look into that won't build up gullys and won't have a spine that is raised down the middle?