Linux for Leftists

I have a feeling that keyboard compression gloves would be helpful to you.

A lot of finger pain and strain comes from over usage of the carpal tunnel and wrist muscles, so you could eliminate a lot of pain by using keyboard gloves and taking 1-2 minute breaks to relax your hands every 20-30 minutes.

Perrix offers a split keyboard that I've been using for 20 years. It's modeled after the Microsoft Natural elite keyboard that was discontinued.

In addition to hardware recommendations that others make, if you aren’t using Dvorak it may help. The evidence is entirely anecdotal but it did help me.

I'd go for something slimline. I don't know how people use chunky mechanical keyboards.. That said, there needs to be some clearance. I used a macbook with the butterfly keys and that was attricious.

I used a Cherry ultra thin usb keyboard and it wasn't too bad. It's not ergonomic, it's just thin like a laptop keyboard so there's not much distance to press down.

Have you considered that it might not just be your keyboard? Four things that made a real difference for me:

1. An upright mouse.
2. Dictation software. It takes a while to get used to and putting on a rhotic accent can help if you don't already speak with one. The one built in to OSX is better than the one built into Word, but it may depend on what you're writing about. Expect copious editing – which is where the upright mouse comes in handy.
3. A lumbar support cushion. This will help your posture so there's less strain on your neck, shoulders, elbows, and wrists. Mine is cylindrical. It attaches to my office chair. You don't have to get a cylindrical one but don't get one of those cheap mesh things as they don't provide any support. You could try wedging a rolled up towel between your chair and lumbar spine to see if it helps before forking out.
4. Set up your office chair so your feet are flat in the floor with your knees bent at roughly 90°. Sat upright, your shoulders should be relaxed and your elbows should be open at roughly 90–100° and your wrists resting on either a dedicated support sponge thing or a rolled up towel. I had to cut an inch from the desk legs to achieve this; otherwise either my knees were too low below my hips, my wrists too high above my elbows, or my traps were tensed up. When you're sat upright, put an arm straight out; you should just be able to touch your screen. Make sure the screen is titled upwards and the top of the screen is below your eye level.

Hope this helps. It makes typing much more comfortable.

Maybe something specifically designated as ergonomic? I don't know too much either, but I feel like when my wrists and elbows are in awkward positions my hands and fingers tire out faster.

Here's a tool for different keyboard layouts that you can do analytical tests with to see which one you like.

When I get around to making a custom keyboard, I want to try MTGAP.

Here's an awesome split keyboard GitHub repository with a lot of information that may help.

I'm not sure how ergonomic this is, but it is a very unique design that enables insanely fast typing speeds: CharaChorder One.

On second thought, I would not recommend the CharaChorder, especially due to poor customer support, the double key press bug, the closed source firmware, and the fact it is still $299. I would be interested in an open source alternative, even if I had to build it myself.

Charachorder did respond to the video saying they fixed most of the issues, but if the device still has closed source firmware, that would be a dealbreaker for me, especially since you cannot remap keys at the firmware level.

I use ErgoDox EZ, and it really helped me with pain. Although my issues were in wrists and elbows, so not really sure if it will help you. But if you are getting a new keyboard anyway, I would highly recommend something with split design like this, it is much better.

Kinesis advantage if you just want to buy it and be good or something like a dactyl manuform if you're interested in a more diy route (although lots of folks sell them prebuilt too)

And switch to a better layout like colemak dh mod or something (basically anything is better than qwerty, past that you get into diminishing returns)

Logitech Ergo K860, kinda pricy but I use it myself and can vouch for it. Very comfortable.

Perhaps try Dvorak style? Once you relearn how to type it's faster and more comfortable for fingers IMHO

I shelled out for a ZSA Moonlander and I can't recommend it under any circumstances. It seems like it was designed by a tech bro, not someone with an understanding of anatomy. I unloaded it on eBay after a few months of worsening wrist pain.

I kind of like Cloudnine's ergoeomic keyboards. They're fairly inexpensive for a split mechanical keyboard, but I like most things about them. There's a full size (huge) and a TKL (merely large).

The configuration software is Windows-only, and also not very good, but you don't have to use it for anything.