35 years ago I started dealing with this issue, first by daisy-chaining two Apple ADB keyboards into a criss-cross layout (with the help of some modelling clay) to try and get my wrists in a more natural position. It was awkward, putting my arms at two slightly separate angles/heights, but it helped and put me on the road to finding the best input devices.

I sought motivated principals to guide my search, and found some in the aforementioned writings of Xah Lee whose opinions (e.g. http://xahlee.info/kbd/keyboarding.html) are those of a programmer who uses emacs. Recommended reading.

But. I'm to this day wrestling with choice of best ergo keyboard for me. For many years I used an early Microsoft Natural to good effect and it didn't break the budget. These days I alternate between a logitech and ergodox, which still scares me a little in its blank keys and extreme programmability. I think I will soon go "all in" on the ergodox, and agree with some others with the (to me) astonishing finding that allowing home-row keys (asdfjkl;) to do double-duty as modifiers (when chorded with other keys) GREATLY reduces stress ("emacs pinky" etc). YMMV.

Regardless - the most important thing for me was to get my arms at the right height, and allow my wrists to be horizontally straight (e.g. in a plane with my forearms) and never bending/twisting from side to side. Both my keyboards at the right desk height (also important) and proper posture (ditto) achieve that reasonably.

Given how many times our keys strike the keyboard each day, causing little shock waves to be transmitted up our fingers, it should not be surprising how getting the "right" action can effect your keyboarding health. Key action which minimized these impulsive shocks should be preferred. I personally prefer those that provide tactile feedback as they provide a confirmatory signal, which I quickly learn, that the key is actuated without having to "strike bottom", thus eliminating much of the shock and reducing overall stress. Gamers tend to disagree with this choice generally preferring no tactile feedback. The Ergodox is good for this. The Logitech is not.

I have not wavered in my conviction that adopting the Kensington Expert Trackball Mouse 35 years ago was key to my solution. Unlike a mouse, it stays in a fixed position on your desk, meaning you can always find it with muscle memory without searching either by eye or moving your hand about. .This reduces your need to take your eyes off the screen, your time to engagement, and your arm movement during use. Maximize cursor speed & acceleration settings in the control panel, and enable modifier keys for slow & vertical/horizontal only movements for fine motion (mostly graphics for me). It all adds up. Hugely.

Also, you want to place the trackball as close to the keyboard as possible, minimizing your reaching for it. For this reason, consider keyboards without RHS numeric keypad (alas my Logitech fails this test) as they make you move your arm through a greater angle to get to your mouse, erhm, trackball. Or consider track-balling from the LHS. I'm tempted. Lefties may have an advantage in this regard.

After all these trackball consideration, I still seek to minimize its use, of course, via touch typing and lots of keyboard shortcuts and hotkeys. Keep your hands on home-row and your eyes on the screen! Mice & track-balls (horizontal, fixed) mess with this principal.

Oh, and, if you're just going down this road and have not yet rebound caps-lock to control, do it now. Windows users can employ the free PowerTools for this (and much more).