What to wear under strapless dress?

Your seamstress can sew cups in for you. It's usually the best option.

Daughter had a pretty similar issue (although her dress had thin straps and a very low back). She's tall and thin, but has a 36 DD chest. She wanted her chest "lifted up" into the natural cups built into the highly structured bodice of her dress, but did not want to, in her words, look like "the St. Pauli's Girl" logo with major cleavage. Like you, she tried every bra option we could find and nothing worked. Finally, in alterations, her seamstress suggested something daughter NEVER thought would be needed.... They actually added TWO sets of cups/padding to her dress.... As a 36DD, she's never needed "padding" in her life, but it was a miracle. The seamstress sewed one set of larger "push-up" cups/pads low into the dress' built in breast structure. Those cups were directly below daughter's breasts, so they provided the "lift" daughter wanted, but that left some gapping in the upper part of the dress' structure. The seamstress used a much smaller set of cups/pads (and I think she may have even cut them down a bit) to fill that space. She was careful to place both sets of pads so they didn't push daughter's chest significantly inward, so NO St. Pauli's Girl cleavage.... The padding helped get daughter's chest exactly where it needed to be within the dress' built-in structure and held her there securely for 12 hours of dancing, hugging, you name it. Like I said, she never expected MORE padding would be the answer, but it was genius. She actually had a couple of girl friends who made a point of telling her how amazing her chest looked in her dress.... lol Work with an experience alterations person and they should be able to make your dress fit you perfectly! Good luck!

Daughter's alterations were handled by her bridal salon. I'm sure we paid a premium for that, but we felt it was well worth it. The alterations woman had a bunch of options for cups at her fingertips, so we just let her figure out what to add to daughter's dress. The alternative to "adding padding" was to completely take the bodice apart and remake it to fit daughter's natural assets. That would have cost a lot more, and once the alterations dept started taking the dress apart, there would be no "going back." That wasn't worth it to daughter, so she went with the "add padding" option without regret. Her alterations, for adjusting the bodice and a bustle (3-point over bustle for the tulle/lace layers and a 3-point under bustle for the lining layers on an a-line ball gown) were about $450 total (no hemming issues...). It was a lot, but at some point we just said, "Okay, go for it...." We just wanted her to be happy with the way her dress fit and didn't care about the details anymore.... Good luck!

PS -- if you do have to buy your own cups/padding, look at any store that carries sewing notions, so Hobby Lobby, JoAnn's, etc., or look online. Google "push-up pads/cups" and you'll find options, but I'd check with your alterations person first. If they have stuff in stock, they'll just charge you for what they use rather than you buying a bunch of stuff that isn't right. Good luck!