I sleep on my side and still much prefer a hooded bag in cold weather. You just can't use any of the brands with no bottom insulation or that hold the sleeping pad in a pocket. Since you're looking at a WM- no problem. I find I can sleep comfortably in my 0 degree bags into pretty mild temperatures by opening up the bag's zipper and wearing it like an open quilt.
Continuous baffles also help with comfort range. You can shake most of the down into the bottom of the bag for mild nights. WM bags are so light there's not much weight penalty for carrying a winter bag instead of a 20 degree bag.
My good down bag is not a WM but the specs are similar. It weighs less than any of my older 20 degree synthetic bags.
