I ordered one of these Sleep Innovations Dual Layer 4-inch topper (2in of memory foam and 2in of microfiber fill). $175 from amazon. I figured I'd put it on the junk mattress that came with my Georgetown and try it out. If it didn't work I could always put it on a bed in the house or give it to somebody and I wasn't out that much money
It works great! I've slept many nights on it (I bought it late in 2010) and so far I've never had an uncomfortable night sleep. I was miserable on that mattress before I put this on.
I bought the queen size, which should be to long, yet it seems to fit just fine on my short queen mattress. The memory foam is removable so you can wash the thing. However I only wash it once per season or so. I just leave it on the bed and put a normal thin mattress pad over top of it, and I remove and wash the normal mattress pad whenever I change sheets.
If you do buy one make sure to read the directions. The memory foam is rolled so tight that you have to unroll it and let it sit for a couple days to reform itself to full size. When I put mine on it was near freezing, so it might not take as long to retain it's normal size if it's warm where you are.
Amazon.com: Sleep Innovations Dual Layer 4-inch topper, Queen: Home & Kitchen