Bra's

If the front of your dress is more or less covered boob tape would work. That's what I'm doing for mine - from perkypear. I would just advise to trial it a few times before the day.

Can you get cups sewn into the dress?

Also, have you talked to the alterations people about it and asked them what they think is best? With a larger cup size, you need to make sure that you can still have enough support with the altered straps, and an expert is the best person to tell you what the various options are.

If you can get cups and boning added that would be the most comfy got. I didn't have time to alter and didn't want boob tape as have read stories of reactions and skin damage so I got a stick on bra which had padded cups and it was amazing, held all day and helped feel the dress was fitting as before it felt like my boobs dropped when I sat down! The dress did move away from me slightly but with the bra my boons stayed in place which felt much better. I got this one, I am 38B so got a D as per the sizing chart and was perfect fit. The tabs are clear and do not show on your back as they are stuck to your side