Alexander Technique worked for me. But it is not miracle cure, you have to work on yourself to make it work. A one line takeaway is that you're probably doing something too hard as a matter of habit when typing.
I like it in theory but I find it hard to put into practice. I have very poor awareness of my body so when others recommend changes I usually feel like I'm already doing it the way they suggest. It's the same reason I sucked when I tried to learn swing dancing.
That's why it's necessary to have an AT teacher for a while, to help you develop awareness of your posture, etc.