I've been using a garlington insulator (retail) with some grip clips (very light ones not the heavy black edge cliping kind) and then use whatever you have in your backpack for insulation. I use a thermarest pad with one of those crazy creek type sleeves for it (gives double use for the pad as chair and insulation). Also extra clothes etc. and I've used a CCF pad also. This has worked fine for me down to about 35 ish. Here's the links to the insulator and the clips I'm using.
www.2qzqhammockhanger.com sold as underquilt protector in hammock accessories tab.
http://shelter-systems.com/gripclips/ click ordering tab and go for the smaller clips.
The Big Advantage! This is really light, packs small, and is cheap. I do most of my hiking in the Southern Appalacians during 3 long seasons. If you're car camping, base camping, or are made of $ then you can probably do better. If you're camping in the snow then you prob. need more. I'll put up some pics next time I get it set up. I've tried down underquilts and a pad inside the hammock. They're either uncomfortable or just pack too big and heavy. GET DOUBLE USE OUT OF EVERYTHING YOU PACK!!