Go to this link http://www.wiggys.com
I bought two of his bags (an Ultralight and a over bag, he calls it FTRSS or something like that). The ultra light (rated at +20 degrees F and costs around 150.00) and can zip into the overbag (144.00 and rated to 35 degrees F). Or you can turn one bag inside out and zip both bags together (I do this with my wife and give her the heavier bag), or you can use them independently. If +20 degrees isn’t enough insulation get the Super light (166.00 an 0 degrees F). You get the picture. Wiggy offers amazing customer service and sells other stuff too.
My wife and I have both lived in the area the weather has a mind of its own. If you stop by the “Railroad Blues” in Alpine tell R.C. Biscuits said hi.
Biscuits