Great at first, worse and worse as the years go on

I bought an Englander "Nature's Finest" mattress years ago, and it conformed to our bodies after a few years and we just keept sinking in further over time. It became more and more uncomfortable to the point I have thrown my back out 2 times sleeping on it. I recently got a memory foam topper for it and it doesn't help a bit. I don't have the receipt, and it's now just past the 10 year mark anyway. Maybe they have gotten better over the years and last longer now, but I am finally looking for a new mattress and will not be getting another one of these.