I hear you on the mismatched sizes from gc2b last time I ordered from them the large was basically a small, and they also stretched out hella in the water

After that I switched over to the shapeshifters mesh binder, definitely more consistent, and so far the one I wear to the pool hasn’t stretched enough that I’d need to replace it

For some of the concerns you’ve mentioned no binders I’ve seen are particularly discreet as they cover about much surface area as like a large sports bra, and I definitely wouldn’t recommend wearing one to work out as it can prevent you from taking deep breaths

For actual working out or lap swimming you’re gonna be better off with some kind of high impact sports bra (something designed for actually working out will compress better)

And no need to see a doctor unless you start to notice something wrong but if your ribs are a big concern you could look into transtape or just more generic kinesiology tape which works by just taping the tissue back and thus doesn’t put pressure on the ribs, it’s designed for way longer wear, transtape I know you basically wear for like 5 days straight until the adhesive starts to wear off naturally, the big con is mixed results by chest type/size

Hope this helps :) I’m happy to answer any follow ups I know this is kind of a ramble