Victoria van Gale here- I'll answer this one. It will be a fun little science lesson! You see, woffs really don't need to be much more than a ball of fur and a tail, as any more than that would weigh them down.
Most of the woff's actual body is filled with a series of air sacs, or 'flight bladders' as they're called. The air inside is heated using the woff's metabolism, reducing its density. This allows the woff to float much like a hot air balloon, while it uses its tail to steer! In addition, woff fur is one of the softest, warmest furs in the animal kingdom- It helps them conserve their all-important body heat at high altitudes.
A woff's lifestyle is also totally adapted to life in the air. In fact, they even eat 'on the wing', as it were, by catching prey mid flight and foraging from sheer cliff faces. Woffs only ever need return to the ground to sleep or lay eggs.
I hope you find this answer enlightening!