I'll join the others and opine your problem was 90% the air mattress. Uninsulated mattresses on cold ground will pull heat away from your body pronto. You can get away with one if you're sleeping on thick, dry forest duff since it can be a pretty good insulator, but that's something I never see at 10k feet, myself. A very thin (1/8-inch) foam pad would probably add enough warmth to keep using the air mattress, otherwise I'd suggest an insulated mattress instead.

Sleeping atop your pack or any other available soft gear might have helped that night. Also, do you know the Ultralite trick of shifting the down to the top for colder nights? It has continuous baffles to help widen its temperature range (very helpful for warm nights).

FWIW I've had my Ultra comfortably below 20; it's a bag I trust.

Cheers,