Take a look at Sierra Designs Diamond Spring 30 (2.4 pounds; $219; sierradesigns.com). It's the ultimate bag for a fetal sleeper for a few reasons. First, the bag's stretch baffle design allows it to move wherever you do. Second, the continuous baffle construction keeps the 600-fill goose down insulation from migrating through the bag and creating cold or hot spots. The mummy design has an ergonomic hood, a tricot-lined footbox to keep your toes cozy, and a pocket at the chest to stow away important valuables. If you sleep colder, try the 15-degree DS 30.
The GoLite Adrenaline 20 (1.12 pounds; $325; golite.com) is another excellent choice. This 800-fill down mummy bag has a unique center zipper, which stays comfortably out of the way when you're sleeping on your side. Plus, it's about a half-pound lighter than your average 20-degree bag and will compress down to the size of a small shoebox.