Ifs a beautiful dress. What size are you? I've got quite a large cup size and that dress would show my bra. I would wear one like this that has a lower cup. I would also look to use some clothing / double stick tape to fix the dress to the bra so it didn't move.
The bra below is a push up so would give you some cleavage. Not sure if that's what you're after. If not look for a bra that has a lower sitting cup. Depending on size and support needed a bralet may work? Bravissimo sell them but I've not looked.
www.bravissimo.com/products/deco-bra-fyn2/#sand-fyn2nu