double up. Two foam pads layered are warm, or one foam on top of an inflatable, or get the cadillac of pads, an Exped Downmat (expensive).
In winter I use two RidgeRests, one full length, one 3/4 length. Warm enough for me on frozen ground, but then I have a sleeping bag that does have insulation on the bottom, unlike those Big Agnes bags (which I think is where your problem starts). 30 degree nights aren't anywhere close to the temps I would need a second foam pad.
