Well, since controlling heat loss might not be easy in your case (little insulation underneath and tight budget), the trick is to generate enough heat for a long enough time to offset the loss. I use foot warmers or small hand warmers. Large hand warmers concentrate too much heat in one area. Be sure to put warmer inside of something else such as a sock. Try not to sleep on top of warmer. Try to keep them at the sides. Maybe, someday, sleeping bag manufacturers will build little net pockets for these to help with heat distribution. These packets are cheap. You can find these in the Walmart sporting goods section. I keep about a dozen in my truck. They come in different sizes that last different durations. I was just at Cabelas where they had a 24 hour bag. I prefer the bags that last just long enough for my sleep duration. The colder it is out, just add more bags. If you are like me and toss and turn, sooner or later, you will find that your bags will migrate to the same spot. Grab them and re-distribute through your bag. Keep extras handy by your side, in case it gets even colder. No worry - you'll be warm.

Xavier Phx, AZ