I developed RSI (Repetitive Stress Injury) in my wrist and thumb from overworking. Others develop CTS (Carpal Tunnel Syndrome); they're very similar. This is common in tech workers using a standard mouse; we're not meant for prolonged motion at that pronated angle. This is exacerbated when on a fitness desk (treadmill or stepper), since the back-and-forth / up-and-down motion increases such movement on the wrist. It also develops from squeezing the wrists inward on a standard keyboard, especially a compact one (eg laptop). I solved this definitively by switching to a trackball mouse and a tented split mechanical keyboard. The fix has been permanent, and RSI only flares up when I'm traveling with a laptop without my ergo peripherals for a long while. Some resort to compression gloves, but that only reduces the pain; it doesn't remove the source, like ergo peripherals do.
First, let's rule out mice which add ergonomics to the standard layout. These include ergo mice like Logitech MX Master; and vertical mice like Logitech Lift or Logitech MX Vertical. While an ergonomic grip does reduce (MX Master) or remove (MX Vertical) the pronated angle of the wrist, the motion in the wrist to move the mouse still contributes to RSI. Many will use these mice and feel better; but won't get all the way better. I experimented with these for a year (before my deep-dive) and experienced just that. For reference: the "MX" series are their higher quality products; where the non-MXs (eg Lift, M575) are their budget products. In general, I don't recommend Logitech for ergonomics; their products are high quality, but they play it too safe on design, not wanting to dive into niche territory due to the smaller audience. Eg, they don't have finger-ball mice or split keyboards.
The solution is track-balls. Yes, the mice you remember your antisocial gamer uncle using in the 90s. Trust me, these are the solution for RSI / CTS.
First, let's rule out thumb-balls. The next step people often take after a failed experiment with vertical mice, is thumb-ball mice, like MX Ergo Plus (quality) or M575 (budget). They do this (and I did this) because the layout is closer to a standard mouse; just replacing the bottom sensor with a thumb-ball. It's easier to adapt. The problem you quickly face is that moving the thumb that much is as bad on the thumb joints, as moving your pronated hand is on the wrists. Now you face RSI in the thumb. Thumbs aren't meant for that amount of static motion. Nor are they very precise, so users will suffer from reduced effectiveness of mouse-usage. Many swear by these, but those with strong RSI feel the difference easily. I own both listed, and when I use one now for reference, indeed my thumb joints hurt.
Solution: finger-balls. Finger-ball trackball mice have you using your middle or index finger to move a (usually very large, better ergonomics and precision) ball. Therefore, their layouts are much different than you're used to, and they have a learning curve (the reason many don't try). As it goes, the weirder the layout, generally the better the ergonomics (eg SlimBlade Pro being endgame). Now we're talking about the "right" ergo mice, let's compare a few popular options, before we land on my recommended end-game.
Kensington SlimBlade Pro is the latest iteration of the SlimBlade. It has wireless (2.4ghz USB), wired, or bluetooth; it's rare mice offer all 3, so that's a big deal. If you know you want wired-only, you can get the non-pro and save money. But I recommend the Pro, so you can travel easily with it, or use it on a future device you didn't anticipate. The square format takes getting used to, but you'll be glad you did. You'll use all five fingers: middle for ball, and the other four for the 4 buttons as you'd guess. Even though you use your thumb, which I've been dogging, you do so in a downward press rather than back-and-forth motion required by the other mice. Virtually no impact on thumb RSI. And I recommend hovering your hand over the whole device, like Saruman over the Palantir; rather than resting your hand on anything. To scroll, you rotate the ball. As you get used to this you'll find yourself grabbing it full-on and turning it; but you'll slowly progress towards sort of "wiping" your ring finger or middle finger along the edge. Once you're used to the layout, scrolling, and ball - which admittedly takes time - you'll find it difficult to use anything else. And a HUGE benefit of the SlimBlade over the others is it's ambidextrous; meaning you can switch hands. If you do, you'll use Kensington Works to map the keys as mirrored. Personally I switched to my left hand to let my right RSI heal up. But by the time it did, I was so used to left-handed SlimBlade that I never went back.
A properly-ergonomic KB (keyboard) is split and tented. Your arms angled parallel to each other and 90deg, your hands vertical, like a robot holding a box. So the dream KB might look like this; which unfortunately requires modding. So the next best thing is "tented" KBs, meaning angled (via legs or kickstands) as steeply as possible.
First, let's rule out non-split KBs. These are the "vertical mice" of KBs: playing it safe to sell more, but too safe for true benefit. These include Logitech K860, Kensington Pro Fit, Microsoft Sculpt, etc. These are indeed better than standard layouts, as (1) they're generally larger, lending to a proper arm position; and (2) they're inward-angled and slight "wave", improving wrist kink. But they're just not the real deal. The closest non-split I've seen to true ergonomics is Kinesis Advantage2. You can see that huge gap between the sides, and slight tenting by way of the concave keywell. But even that's been succeeded by a true split (Advantage 360, below).
Split KBs are so niche that there's only a handful of purchasable pre-builts. Many split users instead buy DIY home-kits, requiring soldering, keying, firmware, key-mapping, and more. Building a KB can take a week of after-hours time. It's not for most, and it's not for me. If that sounds interesting to you, I'll leave it to you to explore r/ErgoMechKeyboards. These include designs like Corne, Iris, Dactyl, Lily58, etc.
Pre-builts: they're just as good, but much more expensive. Each has pros / cons, but Glove80 combines all the pros. Some have concave keywells, which improves ergonomics for the knuckles and fingers. Some have thumb-clusters; which allow you to map common keys for improved ergonomics and efficiency. Some remove the Function key row, relying instead on remapped key-combos; which factors into preference (I prefer the standard Functions for Jetbrains). Some have stronger tenting, or no tenting. For the ~$price, I used what my checkout screen shows from my choices (brown switches, tenting, wireless, etc).
This is part of my battlestation setup, where I discuss treadmill desks, ergo peripherals, laptops, and more.
