I have similar problems - it's one of the reasons I started sewing. Right now, my jeans are in an inbetween state. They are wearing thin, and I know it's only a matter of time before they tear. I was planning to just zig zag stitch, but I hadn't thought about the issue of chafing. I think I might try satin patches, maybe done with very soft thread - but this is just theoretical, I don't know yet how it would bear out in real life!
I'm interested to hear if anyone has good, working solutions.