Doesn't last, horrible backache after 3 years

we got a queen sized plush mattress at Macy's. Was told it was one of their best Simmons mattress. It felt great for the first 3 years. Then the padding on the mattress compressed enough that created deep enough body depressions that it started to give us back and neck pains. Due to the design of the mattress, you cannot flip it. Simmons will not replace under warranty since the body depression is <1.5in according to THEIR measurements. We do not weight that much (wife 100lbs 5'2, husband 160lbs 5'11"). For the surface padding NOT to last even 3 years with such minimal weight is just horrible. Their 10year warranty is a joke. We could not afford another mattress so we tried to compensate for the body depressions by placing folded towels in the depression trying to straighten out the surface, to no avail. STAY AWAY FROM THIS MATTRESS.