A good pad to use would be a blue roll up closed cell foam pad you can buy at walmart. They are actually sold as "yoga" mats but they should work especially if you use two of them. The problem with air matresses is that air is not a good insulator, especially when it moves. Another cheap option, although not comfortable, is a silver coated windshield reflector. The ones people put in their car to reflect sunlight, these can be bought at walmart for cheap. I spent a night out a few weeks ago and used one of those silver mats and a closed cell foam pad that was a half inch thick and was fine.
I was at the Mart the other day and they had 2 styles of pad in the camping section. One was solid but shorter than my height. The other was almost the right size but it was ribbed... Had gaps on top and bottom.. I opt'd not to go with either. Will check out the selection at Gander tonight and I will also cruze by the Mart to check out the Yoga pads your mentioned.