It is encouraging that you found yin yoga to help you with pain during sitting in meditation. My meditation practice has been to sit in a chair rather than on the floor, and I have certainly found my back problems to interfere with that (and not just recently, either. For years, as my muscles relaxed during meditation, I would become aware of the lateral bend in my spine and need to readjust). I expect as I continue the practice, yin yoga will help with my own physical difficulties in meditating.

So now my only real problem is figuring out where my yoga leaves off and my meditation starts. ;-)

I’m not sure it really matters!

I sort of moved into this practice in the reverse order you described. Sitting for more than 20 minutes in meditation started to prove difficult for one of my knees. One day I decided to try a few minutes of yoga before sitting. Of the poses I tried, the one that made the biggest difference was Half Pigeon. Since I like to sit early in the morning, when my body is stiffest, I would do Half Pigeon for seven or eight minutes on each side. Not only did it eliminate my knee pain while sitting afterwards, but I found, as you suggest, that the steady tensions and discomforts of Half Pigeon provided me a mental focus point for meditation, as well.

So now my only real problem is figuring out where my yoga leaves off and my meditation starts. ;-)