The Great Depression of Mattresses

We've had this mattress set for less than three years. At first, it was heavenly. It didn't take very long for indentations to develop in the gel memory foam, though I accept that happens. But the innerspring level began sagging after about 18 months of use. Now it requires physical effort to roll out of the "canals" we've created on both sides of the mattress (neither of us is overweight, so it hasn't dealt with extra pressure). The mattress is " no flip," which basically means that you are stuck with the same side through the life of the mattress. We loved our last Kingsdown mattress, but this was a substandard product for any manufacturer (much less one that charges more the $2K for a mattress set).