I posted a while back about my experiment with a $5.00 Walmart comforter made into an under quilt. I had a chance to test it out this weekend in low 30 degree temps. It passed with flying colors. Warmest I've ever slept in a hammock.
I'm not a backpacker. I either car camp or , more frequently, camp out of my kayak. An extra pound of weight or a few more cu in. of volume don't bother me much. It's folded to give a double layer of insulation. The finished full length UQ is 45" wide and stuffs in a compression bag to about the size of a volley ball.
I used simple cord for the suspension. Very little fiddling to get it to hug the bottom of the hammock. The full length gives a lot of leeway in how it fits.
It probably wouldn't do for a backpacker, but it suits me fine.