I bought some dense foam sleeping pads from Gander Mountain when they went out of business. Extremely comfortable on our cots. Cost about $25 at the time.
Mondokings by Thermarest for us.. They are around 4" plus thick with a very high R rating. We put them in the Northern Lite cab-over truck camper to replace the regular queen bed style mattress that it came with. The Mondokings are very comfortable, warm and very light relative to a bed mattress and off course you can fine tune the air pressure to suit the individual. The best thing is they are easily folded back to ensure any condensation that may have formed underneath dries out during cold weather camping. We previously had issues with under bed condensation despite the Northern Lite being a well insulated 4-season camper when we were out and nights were well below freezing...some near 0*F.
With any inflatable mat, the valve should be left open if they are inflated and you are traveling. Changing elevation when you go up a mountain pass will severely over-inflate any air mat and possibly ruin it,