Ad2knit, I admire your perseverance!
You're getting lots of good suggestions here. I hope something can work for you!
I think Jan is onto something, if you are using straight needles. Try a 24" long circular needle, which you can use like a straight needle, but requires less torque. With a straight needle, much of the weight of the knitting ends up down the shaft of the needle, and with every stitch you are lifting that weight, which is made more difficult because of it jutting out from the hand. Circular needles carry the weight of your knitting on your lap, relieving much strain on your hands. I suggest a 24" length because then you will have a needle shaft that is long enough to hold easily. The shorter shafts of the 16" needles require a modified hold for most knitters, which might be a strain for your hands.
Still, I'm wondering: is there another root source of your pain? Different causes require different solutions. If it's arthritis in your index finger, for instance, you may need to address that directly. (Grumpy Grandma, did you say you take turmeric for inflammation?) A modified yarn or needle hold may be in order, as you have tried. Another idea, and it doesn't seem to me like index finger pain would necessarily benefit from these, but check these out (scroll down to the bottom of page).