Just keep in mind that some David's Bridal dresses don't fit the same as other stores that do more vanity sizing.
I recently bought a David's Bridal dress that's a 12 and it fits me, so a 12 should work for you. However...I'd wait as long as possible before ordering because you never know what might happen.
What if you order a 12 and then injure yourself so you can't exercise as much as you like?
It's hard because I know you want to buy the smaller dress as motivation, but it's better to have a dress that fits/needs to be taken in vs a dress you can't fit into.
That's the advice I got on this board when I had to buy a bridesmaids dress a couple of years ago.