We use a picnic rug underneath the airbed, a fleece blanket on top covered with a fitted sheet and then our sleeping bags. I notice we still get damp patches on the airbed though, so each morning we have to strip everything off and air it off.
Carpet underlay - OH is a fitter and has cut a piece to fit each bedroom. The kids sleep directly on this (with a sleeping bag). Takes a bit of space but worth it.
As we are both wrinklies we use a picnic blanket under the airbed and a single 4.5 quilt on top but under the sheet - covered with a 13.5 kingsize quilt!!!
We have a footprint ground sheet under our SIG and we find this is enough under the mattress. We then have a foil backed picnic rug held in place by a fitted sheet and our double sleeping bag on top. Never been cold.
We use an old sofa throw under the bed, a single duvet or folded out sleeping bag on top with a fitted sheet, then sleeping bags and then a fleece blanket or two if really nippy.. Works reasonably well, and we have an old groundsheet that will be coming back into use next time so we can have the throw as a rug. :)