Being between sizes on one of the most beautiful dresses I've ever seen
Argh I know the feeling! Have the same problem with jeans all the time, Sucks! The local alterations store is your friend though lady. Pain in the butt to have to go in and get it all pinned and tucked but worth paying an extra 30 odd bucks to get a perfect fit if you really love the dress.
Or like Caesar said, theres always the cheesecake route lol