How can I (F21) convince my mother (47F) to leave me tf alone about bras?

Long story short: I have been CURSED with bigger breasts. I cannot stress how much I hate these things. They get in the way of everything, including my sleep. Even with bras that cost $60-80 each, professionally fitted, I was in so much pain with bras, that I would CRY. I am serious. Bras caused me so much shoulder pain, it was like being stabbed with a knife, especially in my right shoulder.

I graduated high school and so stopped wearing a bra so often. Like magic, my chronic shoulder pain went away, and I've refused to wear a bra frequently ever since. And even then, it's a thin one that more so exists then actually does anything. It's super thin and it's the only kind I tolerate.

I do wear a bra when I go out with friends and at work, but I don't wear one inside the house nor do I put one on just for the dog's ten minute walks (or a quick trip to the dog park that's literally right behind our place). So, for most of the week, and most of the time, I'm braless, and this is something my mother just can't stand.

Every few months she and I got into an argument about fucking BRAS. Out of all the things to get into a cat fight over, it's BRAS. I'd laugh if it wasn't so annoying. She says she'll get them herself if she has to, and she'll do research to make sure they aren't so annoying, but I 'need' to wear one for most of the day.

She talks about how unhealthy it is (she states I'll have back issues), and how my boobs are going to sag if I don't wear a bra. I respond that my back and shoulders have actually IMPROVED since I've graduated high school, and so do not wear a bra for nearly the entire day, and that I don't give af about my boob aesthetics. I want these things gone as soon as possible anyway, and am going to get a reduction when the funds are available. So, again, I don't care if they 'sag' until then.

I'm honestly surprised she's spewing such outdated bullshit, and it's making me wonder if she genuinely cares about my health or if this is some roundabout way into making me look 'decent.' The only research she has brought up to back up her health-related claims about magical, magical titty-traps are that she's a nurse, which is bullshit. I respect her profession, and she is a genuinely good nurse, but I am about to snap and tell her that her being a good nurse does not mean she knows every little thing about medicine.

She refuses to get off my ass and I am about to lose it. We have a no screaming rule, but holy shit, can we have a "Stop bringing up the same bullshit every few months, because I am not changing my mind" rule? It's like she thinks she can wear me down if she keeps bringing it up, like I didn't inherent my stubbornness from her.