I use down top and bottom quilts with my hammock. I can go to ground if needed, by using a Cabela's self inflating pad (from pre hammock days), and my top quilt. My hammock is a bridge with double layers, and found that the pad inserted between layers works great to flatten out the lay. Un-inflated, with valves left open, and run a normal under quilt below the pad. Have never felt the cold from the underside. Pad travels with the hammock, compressed and rolled into its own bag, unless space is tight, or weight is an issue. If without the pad, I just use a normal under quilt for the bottom insulation.
Prefer to hang, but there have been times when having the pad with me has allowed going to ground with my top quilt.
My pad is a Cabela's Alaskan Guide, 30" X 80", and is 2.5" thick, with an 6 R-Value.
I like the big pad, as the lightweight back packing pads are just to small for me to have a comfortable sleeping experience.
I bought my top quilts extra long and extra wide, with the enclosed foot-box, and they work great with either the hammock or just the pad.