A close friend of mine has always been buxom. About twenty years ago she had a mastectomy that removed one of her breasts. She lived for many years with only one breast but as she has gotten older she felt the need to wear a brassiere full-time... something she'd done when she was younger and got a fair amount of attention because of her voluptuous figure. When she tried to wear a brassiere with only one breast it simply didn't work, and so she for the first time began wearing a prosthetic breast form. I don't know if the prosthetic is as heavy as a real breast but she is always happy to get home so she can take off both the brassiere and the prosthetic.
My breasts continue to be quite firm and I guess they're small enough that I don't have the problems men here are discussing. I still enjoy wearing a brassiere, of course, but that is as much aesthetic and erotic as essential. Different strokes.