I would say go empire line for it - I know that I'd just need a size bigger right now, and I'm 5m gone. Actually, I could fit into a wedding dress like my own right now and just squeeze everything in, but it wouldn't be that comfortable. Plus I'm so not a size 6 any more! It was a squeeze at Christmas, so I'd probably need a bigger size, but I could still get away with corsetted things.

It would be worth finding a shop that would let you buy something "off the peg" a week or so beforehand, so that you know it fits well. You could also do one of those corset-back things with the lace running up it, so if you need a bit more room you have it.