It's good that you're doing yoga - I find I can run and walk with fewer niggles when I pay attention to my posture and to good form. I found Danny Dreyer's Chi Running book good (he also has a Chi walking one, haven't looked at that) but a lot of the "core" ideas (in every sense of the word) are also things that come up at yoga. You might also want to see a physiotherapist about exercises you should be doing to maximise strength or flexibility in specific joints. And maybe check if you need any orthotics as well as good shoes.
I find forest paths easier on my ankles and knees than concrete or asphalt, but I couldn't use the Couch to 5K podcasts in the woods because the terrain keeps changing and it's hard to dose the effort precisely. Beginning runners are supposed to avoid hills entirely (hard on the achilles tendons etc.) but I found it hard to avoid hills AND hard surfaces. (In a city built on 7 hills, I live behind the eighth.)
I also found that Couch to 5K progresses quite quickly - probably much too quickly for anybody with pre-existing issues. I jog 5 - 10k a few times a week now - but it has taken me an entire autumn, winter and spring to get that far, and I was already dabbling a bit with jog-walking in the summer.
I'm just back from a run now - up through the twilight forest to the big plane tree that stands alone in the meadow at the top of the hill, down past the monastery and the cathedral to the river, along the river on the towpath and then up through the suburbs to get home as the rain got heavier and the night darker.
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