Thanks for the suggestions!

After thinking about them for a bit, I'm wondering if I might try to cut off the top part of my current mummy bag and go for the down jacket option. I'm pretty handy with a sewing machine, and this would limit my financial outlay as well. Maybe I'll sew in a couple of anchors for suspenders or something so I can put it on like trousers. If I can preserve the upper part of the bag, maybe I can make something out of the hood part too.