Sustainable bras: help

I’ve been natural-fiber-focused for many years.. but I have not been able to transition my bras to natural fabric. I typically wear bras from Aerie (specifically Sunnie full coverage) and have been really unsuccessful finding a cotton bra that has a good fit.

I have a few cotton bralettes that I like.. but I don’t feel like the “cups” fit me right. It seems like the bras sort of.. pull apart in the middle and fall to the outside of my breasts.. creating “spillage” in the top. Does this mean they’re too small for me? I’m a 34DD and tend to buy them “tighter” for the support.. but if they’re falling off, I guess it doesn’t matter anyway.

Looking for budget friendly suggestions or help with finding my right fit/size. It’s taken me years to find my favorite bras but it seems silly to have a 98% natural fiber closet just to strap plastic on my chest every single day.