Have you considered a quilt? Or if you mummy bag unzips 3/4 length you can try using it as q quilt. With a proper ground pad (ccf or down inflatible) I would think you could make it through shoulder season without a problem. I have a RayWay homemade quilt with draft stoppers that I use in my hammock (even in winter, although...I do live in Texas, my lowest temp has been 23F) and I don't have a problem with coverage or have to wrestle with it like I do my mummy bags.

Tango