Fell for the "hipe"

When I first got this mattress, my back did not hurt anymore in the morning. Almost 2 years later, back aches again. The side I usually sleep on has absolutely lost it's firmness, and if you stand in front of bed you can see the difference in height of sides. This is not what I expect from Sealy, and not from Mattress Firm as the seller.Today I am going to visit the store where I bought it, and see what they tell me about the warranty--which does not show the numbers the written "warranty" tells you to look for by the word warranty........mine just has (99) and not 2 numbers separated by a /.......we will see what Mattress Firm does for me...