I’m 5’7 and 145 pounds and the smalls fit perfect! 32 C cup and I have pretty large lats. Stick to your true size or size down with a smaller cup size because they are not very compressive
I am 5'5, 140lbs and am a 32DDD (28.5 inch underbust). I got a small and it is a nice relaxed fit. Someone with a similar rib size but smaller boobs would probably be an xs. It doesn't feel as tight as the other Small bras from the same company.
Straps aren't adjustable and they were so long that I can't even wear this
Size down if cup size is less than C. I got a size small and I'm 5'7, 145 lbs and a 32 C-D cup. It had a little extra room but fit me well.