Ever use a snugpak jungle bag? Versatile, packable, and can handle temps when used in combination with other gear. Pack very small, light, full unzip to blanket, square, insulated when wet, can find at low cost. Can use two of them up for lower temps, or use a military issue poncho liner woobie, or even a quilt. Also in tandem with bivy, pad, and base layer clothing (ECWCS gen iii, level 1 and 2).
http://www.snugpak.com/military/military-sleeping-bags/1-season/jungle-bag
http://www.snugpak.com/military/military-sleeping-bags/bivvi-bags/special-forces-bivvi-bag
Just the jungle bag inside a bivy is good to pack for emergency out of a spike camp and is super small.
See if you can wear this stuff out. If you do buy some more. Good gear that will last many years, with good prices.
I have mummy bags. I no longer use them for back packing, even late november/december.