took a knee into my sternum hard during a vale tudo style mount. when I heard and felt an audible POP and felt the crack, I knew I was in for bad times. It's been 3.5 months since and still is too sensitive to roll =(. The pain is a lot less than when I first got it injured. Hopefully you didn't actually break a rib. A hairline fracture takes a long time to fully heal so that you're up and ready to roll with your pre-injury durability again.
What I'm doing in the meantime is drilling top game techniques like spiderweb, mount, guard passing, etc. Anything where you don't have any weight on the ribs. Make sure to tell your training partner/s about your condition so they don't turn on the "must crush" mode which could end up re-injuring you and extending your recovery time. Also, don't try to resist body locks. I made that mistake. They just don't seem to hurt enough to make me tap, but your ribs will get damaged if it's locked onto you tight enough. Hopefully this helps man. Good luck recovering.