I did a little searching and it looks like you'll be fine. Apparently, chiffon and voile are the same thing, and that's what the Australians were using when they first started BIAB.
And even if doesnt work quite right, BIAB bags are pretty cheap, like $10 from a brick and mortar LHBS. A paint strainer bag from Home Depot works too
You could use the chiffon as bags for dry hopping too