Jacks-R-Better makes something similar to your needs, and along the lines of Angry Sparrows Comments.
Check our the JRB Down-to-Earth Converter kit.
and pair it up with one of their wide quilts: I recommend the Sierra Sniveler
Add in a FLOT (full length Omni-tape) mod when you buy the quilt.
BAM! exactly what you want. Quilts or a bag, at your leisure.