Backache using mattress

I bought this mattress at Raymour and Flanigan for $2,000.00.  After only 6 years, I have a backache when I use this mattress. When I switched to the other side of the bed, my backache went away. Simmons would not handle any complaints and told us to deal with Raymour and Flanigan.  To replace the mattress within the 10 year warranty period, the depression needs to be 1 1/2 inches. Comfort is not covered and they do not care if I have a backache. I will never buy any thing from Raymour again.