I would say your best best is going with a "fly high" fat sack. So far they have been "pushing" (if tehre is anything to push) with fat sacks. There materials are very nice. They use one solid inner and outer. So insted of having a bladder then a saftey covering its just one solid fabric.
Also, filling and draining isnt to much of a pain. It is obviously nicer to have internal ballast with a flip of a switch, but if you cant manage that... THEN FILL THEM SACKS