Scratch, the extra layers we wore took care of the drafts. We didn't take any measures to hold down the sides of the bag. I think a quilt would be more ideal, but the bag is a very lightweight solution for now. The extra layers are a necessity to bring, so there's nothing we added to bring up our base weight to compensate. The Mountain Light seems roomier than some, as I have wide shoulders and chest and specifically bought it as I can actually fit without feeling strangled. I'm experimenting with using 4 wooden clothes pins that are attached to the pad straps with another small strap and velcro.
This would keep it down when you roll over. Something I tend to do. Please keep us informed of any system you end up getting.