Hi, scruffypuff, Welcome to the forum. I cannot even imagine contemplating a camino with lung cancer, but your attitude surely impresses me. And I of course wish you the very best.
Do you have any idea what would be a reasonable stage for you? Some of the typical Mozárabe stages are pretty long, but most can be cut with accommodation in the middle. If you haven't seen it, I would recommend the association's guide. It's online and updated frequently. Most recent version is July, 2018.
https://drive.google.com/file/d/1TPFLk73vdZwdQZStc925IkfPlTSnVvRi/view They have changed most of their maps to include little houses that show you where accommodation is located all along the stages, and just scrolling through, there are a lot more options to split stages than I would have thought.
I know that on some of the long stages with no in-between stops, some forum members who walked this April took cabs now and then to shorten stages, so that would be an option for you as well.
I can't emphasize enough how helpful the Association members are. You should contact them with any questions, and of course there is a bunch of us here who have walked it happy to help as well. I walked in springtime and have never seen such an amazing array of wildflowers, it was truly unbelievable. Sept. and Oct. are likely to be warm, but of course all bets are off now that the climate seems to have become much more extreme. Buen camino and good luck with this plan. Laurie