Why don't you just buy a controlling undergarment for that little dress?
I have lots of friends who are young and thin but will wear Spanx when they think they need to look a little better! I've actually considered getting some myself... I'm still small too, and anyone would tell me I'm nuts, but there are little things I don't like about myself and I'd feel more confident out in public if they weren't showing! Personally I think I'd want to avoid any surgery or needles putting chemicals in my body at any cost. The risk would probably outweigh the benefit. Unless the stuff has been around for decades, there's no telling what it could end up doing 10 or 20 or 30 years down the road...