A split keyboard might still bring you some relief. Modifiers/enter/backspace/etc are usually moved away from your weakest fingers (pinkies) to your strongest (thumbs). I have Ctrl, Alt, backspace, delete, space, enter and shift all on my thumb clusters.

Here's an example of what that might look like: https://kinesis-ergo.com/wp-content/uploads/KB360-GBR_FRONT-... (though in the default configuration, shift is still on your pinky; you can customize this on most keyboards, or on OS level).

The rabbit hole goes very deep. Another option is home row mods: https://precondition.github.io/home-row-mods. A combination of thumb clusters and home row mods can reduce your finger strain a lot.

Also the type of the key matters for tendonitis. Some have tactile feedback after the key is pressed but well above the bottom so you learn not to bottom out with force.

https://kinesis-ergo.com/products/#keyboards

(They used to have low-force options; perhaps all are low-force now?)

Kinesis also offers custom switch options through Upgrade Keyboards: https://upgradekeyboards.com/collections/kinesis-advantage36...

Lead times are long, and Kinesis products are expensive. It gets a little more bearable if you take into account that you're using this tool 8 hours a day for years and years, but still. Cheaper options exist.

I can't second Kinesis enough. I have been using them for 20 years now. I was starting to have issues and I haven't have a single issue with my hands or wrists since changing over. Also a good vertical mouse will help if you use a mouse much. I use trackballs or vertical mice interchangably.

Ok, fellow old hacker here. I have a similar problem and I found that a lot of the hand pain was from mouse/trackpad usage. My hands have been a lot happier since going to a trackball because I don't do nearly as much gripping and pressing.

Also, a vertical mouse works wonders for similar mouse-related tendon issues.

The angle / position your wrist is when your fingers need to do these lateral movements could be more or less taxing depending.

I forget the name of the layout (the board is a Lily58), but my keyboard does away with the staggered key spacing and has keys aligned vertically with a subtle bowling. You're usually pressing keys with your pad, not the sides or tips, and I suspect it would be even better with flat low profile keycaps.

There are some styles of "chording" keyboards that might help too, and some that would be way worse. Chording keyboard are also wildly different to regular keyboards, totally alien by comparison to just splitting a keyboard.

Give svalboard a look. Might be some old threads on here about it.

https://svalboard.com/

Suggestion, don't use your pinky. I haven't used it for over a decade. Instead, move your whole arm as a unit, and primarily use your index finger. It takes some adaptation, but movement is better than stillness the vast majority of times.

As for the tendinitis, have you tried physical therapy for your fingers? Whenever I've had a stupid day of overusing the thumb with my phone, I wrap the smallest possible elastic band around my thumb, and do some curls. Slow and controlled. The mixture of force, movement and stretching feels great, and the issue is gone.

Here is an example band https://www.decathlon.es/es/p/banda-elastica-5-kg-cross-trai... the important part is that it's really thin and light. It should look like a string, not a flat band.

Maybe a low-profile keyboard with very-light actuation switches could help. Also choc keyboards have less spacing between the keys than traditional MX keyboards, which should required less finger travel.

Using a thumb key for Enter, would definitely help with your pinky.

One thing to try is to sleep with your hands underneath your pillow in a prayer position. If your hands tend to curl the fingers while you sleep all night, that causes real issues eventually.