If you're having tendinitis related to programming, here's my advice, having gone from basically crippled and nearly crying in pain trying to drive my stick-shift car home to virtually pain-free for nearly two decades:
(Ordered from most to least important)
1) physical therapy and exercise. They'll show you stretches, which are probably the single most important part of healing. Later, I got into rock climbing and never had another tendinitis issue related to typing. Go easy, though, and use anti-inflammatories regularly and responsibly. Wrist braces help by giving your tendons a break and keeping them warm, but they don't solve anything on their own.
2) get a better keyboard. A true mechanical keyboard with a light touch will greatly reduced the irritation to your tendons. Lucky you, there are more on the market than ever before.
3) get a smarter keyboard. The Kinesis Classic changed my life. The Ergodox is very similar (both rooted in the Maltron, IIRC). The traditional 87/104 keyboard layout is absolutely absurd. Moving your entire hand to reach navigation keys and using your pinkies for return and tab? Lunacy. Yes, vim helps, but why reprogram your brain when you can just buy hardware that's not rooted in 19th century constraints?
4) keyboard layout. This is the least impactful change. It also takes the most time and will actually increase pain until you reprogram your muscle memory. It has the least payoff. It took about two weeks to type Dvorak with basic competency. About two months to reach what you'd call reasonably fast. And easily a year to get to a reliable 80+ WPM. On the plus side, I can fluently switch between Dvorak and QWERTY.
A lot of the talk online about keyboard layouts is just alpha-geek mental masturbation. Don't think a keyboard remap is going to save you if you're in pain.