Ian, that sounds like a pretty durn good idea to me!
Another idea that is easy to make might be a simple "quillow.
20 years ago, before I knew what a backpacking quilt was my wife made a quillow and although it was quit small I was always amazed at how warm and comfortable it was, because you could stick yer feet inside the "pillow" pocket which kept 'em toasty warm and kept the quilt in place over you.
Should be easy to make one, and it could be tapered to reduce the weight. Of course I'd tie it rather than "quilt" it on a sewing machine the way Ray Jardine recomends his quilts be tied, to keep loft.