I did a quick read through the other replies, so if someone already mentioned something similar sorry....Have you looked at a modular system with a possible bivy sack? I have one for the military and they're great. It gives you two different sleeping bags with a fairly good all weather bivy sack. I'd have to check on the temp specs, but I've used the inner lining bag or patrol sack down to 30 deg F and the whole sytem down past 0 F. You can always adapt to carrying part or the whole system. I have seen them online for around $200-700.