Welcome to Gaia! ::

If you had a hula hoop in the dress, nothing else would be needed to keep it "inflated" i don't think. It'd just pull the fabric taut and that would be that. However, I think a hula hoop in your dress would be VERY annoying at a con. People are constantly bumping into you. They'd bump into the hula hoop constantly and it'd never end up hanging right.

You could always try sewing sewing fosshape into the dress. It's the coolest stuff evar, because it's like fabric, only when you heat it, it gets stiff. Check it out!

http://www.cosplaysupplies.com/wonderflex/wonderflex.html

For that matter, you could make the handcuffs out of wonderflex too! It's awesome, awesome stuff.

I'd kind of like to be a Flonne, meself. ^^;;

That stuff might actually work... My mom says she could sew the costume easily, my dad know what we can treat wood with to make it look like bones (for the necklace, armlets, and bracelets) and my mom thinks she the stuff might work (to bad its alittle on the expensive side) sweatdrop

What staff or other wepon would you be holding?
And i've heard the name Pleinair but i don't rember what she looks like.