I would like to share my own findings after scrounging online in other websites and forums, as well as what I personally experience/practice. Perhaps someone else who has a similar condition might benefit from this as well.
As Costo is a condition in which the cartilages connecting the ribcage to the sternum get inflamed, it has a spectrum, and that differs from one person to another. There won’t be one specific yoga pose or exercise that will be good for EVERYONE with Costo. This is what I practice myself, listen to your body and find your own comfort zone, as why works for me might not work for you.
My affected areas and degree of pain/discomfort varies. And as with most ailment, there will be good days and bad days. Some days I don’t do any yoga/exercise at all, I meditate and try to rise above it. Personally I find that on days when it’s really bad, I don’t do any yoga that engages my upper body. On days when the pain is manageable, I do very light stretches to help loosen the muscles around my chest, and mid and upper back. Nothing that I need my upper body strength to practice… no downward dog or anything that I need to use my arms or upper body to prop myself.
One thing I do say is to listen to your body, if there’s pain or discomfort in the affected areas, stop. Don’t push it at all. Rest the area until you feel better.
My doctor did tell me to take krill oil/astaxanthin to help with the inflammation and as an antioxidant. Skip the omega 6, up the omega 3.
Hope this can help someone else as well.