So the dress has been purchased and it is such a relief to have that out of the way!
I ended up ordering it through Erin Cole in Costa Mesa and while they weren't the cheapest, and are quite a drive from my house, they have a lovely store, great service, and a stunning selection of accessories and dresses (there were actually quite a few that I liked which hasn't happened at any other store I've been to), so I felt comfortable ordering the dress through them.
Another reason I was happy to purchase the dress from them: I was commenting to the woman at the store that the dress had been difficult to track down, and how there was absolutely nothing else like it around, and she told me the story behind it. Apparently the owner of the store Erin Cole and the Rivini dress designer (Rita Vinieris) are good friends and that this dress was actually custom made for Erin Cole's own wedding, after which Rivini decided to add it to their collection!
Their sample was a size 10 (I had previously tried on an 8) and the 10 fit me perfectly/ was a little too lose, so thank goodness I didn't follow one stores advice and order the size 12!
I guess now I just have to figure out the veil, maybe some jewelry and I'm done!