How far along are you now? Just thinking that if it's early hyperemesis won't have had a chance to kick in, so you won't know if you've avoided it yet. If you end up with HG I would say definitely go for the 5/6 months as it might have eased, whereas it is likely to still be very bad at 3/4 months. If you're 9 weeks + though you might have escaped HG, it is rare apparently, but as a sufferer I can tell you that's the last thing I'd want on my wedding day!
I'm normally a size 10 and 5'9, but even with my first pregnancy I was showing noticably by 10 weeks, and it was bump not bloat, consultant confirmed. That being said, even if it's bloat it will affect the fit of your wedding dress. As others have said, my boobs were much, much bigger, and by 14 weeks they'd gone up three cup sizes. I think I might have been a bit unusual in that respect, SIL didn't show at all until she was about 25 weeks.
I got married when I was 14 weeks pregnant, and the biggest tip I would give, as others have said is to have a lace up dress. Also, don't pick a heavy dress as I was in agony by the end of the day as it couldn't be done up tight enough for it to sit properly as I couldn't stand pressure on my tummy, so it kept slipping down, and was generally uncomfortable.
Personally I would have gone for 5/6 months in hindsight, my bump at 14 weeks wasn't pronounced enough under my wedding dress to look much like a bump, so I just looked like I'd been hitting the pies big time, and it makes our wedding photos look a bit weird 