Terrible mattress

We've had this mattress for just 3 years and it is excessively sagging. It actually started in the second year of use, but unfortunately I didn't look into the warranty on it. I think I was in denial that this new-ish mattress was actually deteriorating so quickly. I wish I had as I am now shopping for a new mattress once again. I initially spent about $920 on this mattress and expected to get more than 3 years of use from it. The sagging is so pronounced on each side that it's as if we're sleeping in two holes. I found a 'hack' online to temporarily offer a bit of assistance: we now have slipped a row of pillows between the mattress and the box spring to push the mattress up in the areas where we sleep. It's ridiculous, but gotta do whatcha gotta do. Definitely pass on this mattress unless you like shopping for a new one every 2-3 years.