We recently upgraded from our Chevette "we can sleep on this while we're in our 20s without hurting" mattress to a Cadillac (actually a Simmons Beautyrest Black Grace). It's a joy to lay down now, and we don't hurt at all in the morning, despite da missus being prone to back pain.
Unlike audio gear, my experience says the best strategy is find something you really like that is completely outside your budget, and then wait for it to go on sale, because it will. Ours was a $5000 mattress, and we only had to wait a couple of weeks to get it for $2000.