I don't know if someone has already mentioned this but you could discreetly sew pennies into the bottom hem to weigh it down. They're light enough that they won't do any major damage and heavy enough to keep it from going poofy.
Oooh maybe that'll help mainly in the back! I was slightly thinking something about that earlier but didn't know if that would be silly or work, it's not really hemmed at the bottom but there are two layers, would the pennies show through you think? The fabric is a bit c thru that's why there are two layers.
I was hunting for just this comment! Wondered if anyone else thought of weighing down the back hem to keep the fabric from floating away on you. If pennies are too large for the hem (what a great idea by the way), I've heard of weight chains used in flimsy couture hems. I don't know where to find one. Maybe the pros at the sewing stores would know, or you could get something like the simple ball chain (like for dog tags) from the hardware store, just coat it with something so it doesn't rust your fabric after washing. This is GREAT! Model/ creator and end result are both so summery cute!!