Did you do any winter camping before you took up hammocks? Where you sleep is only part of the picture.
You can double things up. It's "layering" - just like clothing. Use two top quilts. Put a second hammock under the one you sleep in, with plenty of insulation between. Use an extra poncho or tarp to block the wind from the side or below. Car camp - you can't carry (or pull) all this stuff until you have a good system worked out. Test in your back yard at first.