I second the hammockforum recommendation. I would also suggest that you do some trials in your yard. Test out different systems at different temps to see what works for you. When I started winter hammocking, I would watch the local weather forecast and if the night was supposed to be 5* colder than my previous low makr, I would sleep outside and see what my hammmock system did. I am now down to a low of under -10*F and still quite warm. Like Phat,I use a poncho underneath, however i keep it loose and away from the hammock body and put and few large leaf bags with a tiny bit of air trapped in them. (google garlingon insulator) is amazing how well these work.