I suspect you will have to get a specialist bra to achieve success.
It is an engineering problem. Unless the items needing support have enough solidarity to support their own weight against the force of gravity, that weight needs to be supported from underneath in some way. There are no muscles in the actual boobs themselves, and they consist mostly of squishy fat (technical term) Without shoulder straps and clever shaping forming a sling underneath to hold the weight, some kind of cantilever system is required.
Wall shelves are held up by brackets, which transfer the weight of whatever you put on the horizontal shelves to the vertical wall below.
Successful strapless bras do the same thing with a broad firm flat chestband with a shelf attached on which the boobs rest. If being on a shelf raises the boobs up successfully and has them flatter underneath where they rest on it, this can make them look bigger (or give a uniboob effect if the bra doesn't separate them and they spread together like two jellies sharing a plate). this means getting the right cup size.
The bandeau style is only successful on small perky ones which can resist the pressure of the bandeau - not for most of us auld yins.
I all comes to down to £££ in the end.
