My dress has boning and a "seat belt" that hooks around the ribs for extra security. I didn't wear a bra trying it on and it was fine, but we used those industrial-strenth clamps (it was a sample 2 sizes too big.)
Anyway, my first dress fitting is about a month away. I have been looking for longline bras and bustiers because I want to whittle my middle and give the girls support. Everything I looked at had boning, but my dress already has that. When I called the shop for advice, they said the seamstress can sew cups into the dress. They seemed pretty confident in that solution, but I thought I'd put it to the boards.
Did you have cups sewing into your dress? Did it provide enough support? Would you suggest additional undergarments anyway?
For reference, here is my dress, and I am a 36c.

(If you're wondering why I am clogging up the boards today, it is because I'm the first of my good friends to be married. They are all very single and ready to mingle, so they don't have the answers I need.)