I just thought of something you could do. Some singlets have a built in crop top bra. If you cut the back part off the inbuilt crop top and stitched the sides down to the front of the top it would make a pocket. You could insert your prosthetic breasts into that pocket and put a strip of Velcro underneath to secure them in.

Then you could throw the singlet on in one step, have your breasts on and not have a tight band squeezing you like a bra. Knowing that your breasts are securely inside the singlet. If you want it more bra like, you could cut the singlet up shorter.

I hope this helps