Undergarments that are low cut

I had one of those stick on strap less bras that use the string in the front. It worked out okay. I also had spanx as shape wear for my bottom half and to help from chaffing.

Like pp mentioned she if your seamstress can add in the cups instead. I was originally going to go that route but my lady told me I still needed help to achieve more cleavage and suggested I wear the stick on bra. Everyone's body is different obviously so I'd ask the person you would go with for alterations as they would know all the different options to give you.