All of those dresses are gorgeous. Honestly, I prefer the Brianna the most. I find the Ambrosia and Ambrosia look alike to be a little busy. However, I'm a minimalist that likes things clean and un-cluttered. I just had to say my piece.
As for getting a dress online, there's a thread around here somewhere about a website that makes "knock off" designer dresses. It's a shop in China that makes all dresses to your specifications and measurements. That might be the safest way to go. All the feedback I read was very positive. I contemplated getting a dress for myself there. If you truly love the design of the dress, at least it could be made to fit your body (like a glove)!
Good luck. Let us know how everything turns out!