Is there a particular brand name?
We bought a Lucid 16” (not 18”) latex, memory foam, mattress from Amazon. King size was 1K, but it comes with a 25 yr. warranty. We’ve had it for three years and, unlike any spring mattress we’ve ever had, it is as firm and dent free as the day we bought it. As another poster put it you seem to float on a latex mattress.