Our Flippac comes with I think a 3" thick foam mattress. We both found that when sleeping on our side our hips and shoulders would "sink" through and it would feel like we were sleeping on the fiberglass directly. A fellow Expo member recommended using the self inflating sleeping bag pads. I had two old ones only 3/4" thick and 2/3 length. We place those under the mattress sheet inflated fairly firmly and OMG it "bridges" the soft foam and IMHO is more comfortable than our good Ikea mattress at home!