I highly recommend a water bed. I used to sleep on a $5+k mattress which was great. However, pregnancy brought on a new set of aches that I've never had before, like pins & needles on areas that was pressed against the mattress and what felt like a nerve pressing against the pelvic bone, apart from the usual muscle aches. All that stopped on the 2nd day sleeping on our water bed, regardless of the sleeping position. Hubby's body aches (from awkward sleep positions) vanished too.
These days, water beds are anti-wave, firmness can be adjusted & can eeven be heated (good for the elderly). I bought mine at fantasy waterbeds, along beach rd.