We purchased a Serta Perfect Sleeper Island Palm king size mattress. Within weeks we began experiencing back pain and the mattress visibly sagged and the sides were broken down. According to Serta customer service (1-888-557-3782) this is a normal Serta mattress. The warranty requires sag of 1.5 inches when measured from side to side over a 1.5 inch block of wood. I asked how a side to side measurement can be accurate when the sides are part of the problem. They said that it their standard method to measure. The 15 inch mattress is barely... read full review »