I have a backless bra...I wore it on my wedding day! I got it at LaSenza (Canada's version of Victoria's Secret). What it is (for those who don't know) is just the cups....with underwire) that you tape to your body! I'm not sure what Victoria's Secret has, but I know LaSenza had two kinds of backless bras.....one was just adhesive tape that you taped to your body (I don't know HOW that would keep my girls up!) and the other was the one I got, the cups with underwire that you tape to your body!
I think it works amazingly and don't worry about your cup size! My "girls" are...how shall I say this?......well endowed (I'm a D cup) and they held me up all day on my wedding! I wasn't too sure about it to begin with so I did a test. I wore the backless bra one night when I went downtown clubbing with my girls. I figured if it held my girls up while dancing and sweating all night, then it was good enough for my wedding!
I also used it on my honeymoon (I have a backless gown that I wore on formal night of the cruise!) It's a little painful to get the bra off (but I didn't notice with all the champagne I was drinking...lol!) and the only other downside was that there was some glue residue on my chest area (which washed off in the shower...no probs!
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All in all, the bra rocks! I have since bought some backless shirts and can wear them out in public without feeling like I'm sagging (which used to be a HUGE problem for me and my big boobies!
) Give it a try, it's great!