Prone to Sagging

I’ve had this mattress 3-4 years and paid $2k for it. With the manufacture’s box spring; full bed frame support; and continuous rotations every couple of months - this mattress has developed severe dipping/sagging in the sleeping positions. They began developing shortly after purchase and now they’re unbearable. I’m 6’ tall and 190 lbs. My spouse is 5’6” and 125 lbs. This mattress should have lasted about 10 years before needing replacement. I’m looking at replacing after about four years. Junk mattress - avoid!