I know you said you don't want foam, but personal anecdote - we moved from a (queen size - didn't change that) $1k+ pillowtop 5 years ago to a foam mattress from Costco and have found it to be a vast improvement.
Even more important I found that by not using a pillow when I sleep on my back (I still use one when I side-sleep -- the pillow is smaller than I used to use) I no longer ever wake up with back pain that I didn't go to bed with, and even going to bed with a sore back it's usually better by morning.
If you look at what your posture is like lying on a pillow on your back in bed (hint: you look like a hunchback) it's no surprise that it's not good for you.
Main downside to this is increased snoring... but we both snore so she can't complain too much (and she always falls asleep first, and I have audio proof haha).
Unfortunately I do find the foam warmer. Some friends of mine bought a super fancy brand of foam mattress and apparently also got some special gel cover and they say it's cooler than their previous (hated) fancy pillowtop. While ours is warmer, it hasn't bothered me enough to get such a gel cover yet.