Don't worry about staying warm in a pop-up. I've had two, both were toasty down to 19 degrees. Both pop-ups, a Four Wheel Camper and a Jayco, are probably good for even lower temperatures, just I've never personally camped below 19 degrees F.
So far, I've had air bags on two trucks and Timbrens on one truck. Both suspension upgrades have engineering trade offs.
My advice: load the camper on the truck. If the camper sits level (side to side --- not leaning toward the driver or passenger side), get Timbrens. If the camper list to one side, get air bags. You will need different pressures in the airbags to level the camper.