As a woman who has had tons of trouble with bras, I highly recommend abrathatfits.org. It has been a game changer. The subreddit has some great resources as well (not sure if that’s changed since the protests though). But anyways, the majority of women are wearing the wrong size bra and don’t realize it. I went from a DD to an H. I can wear my bra all day and barely notice it. If you’re breastfeeding I suggest measuring when you’re half full. That’s what I did when I was breastfeeding and got the best results.
Luckily you don’t need to go to the subreddit to measure yourself, I’m constantly talking to women whenever I’m able to bring it up organically. I fucking hate what Victoria’s Secret has done to women and bras. One day I swear I’m going to stand in front of one of their stores and hand out measuring tapes and a paper with the website on it. I became such a huge advocate after learning my real bra size. I cried when I tried on my first H cup because I was finally comfortable and everything was in place.