Save up your pennies and get a Kifaru Slick Bag. They come rated at +40F, +20F, 0F, and -20F and they make a wide model. The bag scrunches down to about the size of a volleyball and the -20F bag weighs under 4lbs. while the 40F bag is under 2lbs.

It's not cheap but I've found it to be pretty bulletproof and should last long enough to justify the cost. You can wear lug sole boots while sleeping in it and not hurt the bag at all.

I use my Kifaru for both hammock and tent camping and so far so good. Highly recommend this bag to anyone.