Personally most all of the conventional stuff on Ergonomics doesn't do me much if any good. Health problems can make some stuff difficult, & cause a bit of pain, so I wanted to make a quick post on stuff that folks may not have thought of that help me, in case it helps anyone.
The most surprising has been the move to a mechanical keyboard. They're sold for gaming, & reading very many site reviews I've only seen it mentioned once that they can ease fatigue, & in my case, pain. Most use Cherry switches, or a fairly recent Chinese clone of those switches. The most common switches are classified by the colors Red, which has no detent, Brown, with a very slight detent, & Blue, with a more noticeable detent, & BTW a slight bit of noise. That detent provides tactile feedback to tell you that you've pressed the key far enough to register.
What surprises me is the how much less force or effort is required to press a key, & how that matters. I've always bought keyboards by their feel because I'm very sensitive to that, and didn't think an improvement was possible, & if it was, that it would matter -- I was wrong on both counts.
That said, with keyboards it's important to either treat them as throwaways, or do a lot of research. Many have a surprising number of common defects, and that's just within the 1st weeks & months when folks are more likely to post that sort of thing in a review -- seldom will anyone take the time to say something failed after a year. The ad copy for mechanical keyboards most always overstates their switch durability -- electronics, solder joints, lighting, the coating on the keys [showing the letters], & even the keys themselves all can & do fail.
On a semi-related note, I've found it very helpful myself to use a keyboard drawer setup, & to mount lights on the underside of the desk shining on the keyboard. Of course didn't have a problem when keyboards were computer beige, but now almost all are black. Having the keyboard on the desktop, an equivalent amount of lighting effects how & what you see on the monitor, hence the pull-out platform or drawer. Most mechanical keyboards come with backlit keys, & if you turn that off it's hard to see the letters because they are not white. I've actually found the added lighting more important with backlit keys -- they still show up fine & I have Much less eyestrain. FWIW I use a LED strip light mounted under the desk over the drawer.
One of the most perplexing accessories for me in the mouse. Everyone's different, & you have to find a mouse that's comfortable to *your* hand -- there's no getting around that, & if you don't it'll add to strain &/or pain somewhere, and not necessarily in your hand or wrist. [It's perplexing to me because I might use a mouse for years & then all of a sudden I can't use it anymore because it hurts.]
That said, I've found the hyper scrolling wheels on some Logitech mice great for things like web pages/sites since they have no detent at all. I've found that having any extra buttons on top rather than at the sides helps -- it may not be as fast for gamers, but on the occasion that my hand doesn't behave perfectly I'm not pressing them by accident.
I've found higher resolution mice essential, in the 2000 - 3000 range, though it takes a short while to get used to one at 1st. The higher resolution means you don't have to move the mouse hardly at all -- you don't have to move your whole arm, & if the mouse is small enough, you might even be able to cup it in your hand, & not move much of anything. A mouse with a button on top to change resolution is great because you can easily lower the resolution for detail stuff when you need to.
My golden rule for buying monitors is make sure you can easily give it back. [The one time I broke that rule with a Dell monitor was one of the worst experiences I've ever had, & it's still not over.] One reason is that they can die in the 1st weeks. Another is dead pixels -- they're common enough that you usually have to have x amount of them before it's considered a defect. I can return a monitor to a local retailer like Best Buy no questions asked, but with an online seller I have to ship it, & they'll check it to make sure it meets their guidelines for what's defective.
A 3rd reason is more complicated... LCD monitors are complicated. The way a monitor works may cause you problems from eyestrain to headaches to anxiety etc. When you poke your finger with a pin nerves register pain & that's sent directly to your brain -- most everyone behaves the same way, feels the same thing. Your eyes are completely different. What you see goes through an awful lot of processing before your brain actually *sees* anything. And most everyone's different. So be aware that this sort of thing happens, & be sensitive to any possible effects.
The 1st consideration choosing a monitor, other than price, is the pixel density & size. Pixel density = how many individual dots of color are possible [the resolution] for the square inch or mm size of the display, e.g. a 1080p cell phone or tablet will have a Much greater pixel density than a 1080p 24" monitor, because you're packing the same number of pixels in a MUCH smaller area. It can make a really big difference, e.g. with a 4k TV, or with some cell phones, or it can mean hardly anything, e.g. with most of the things you'll do with a PC. With a 4k TV or high pixel density cell you'll often see a definite increase in clarity & quality, even when the content itself is lower, standard resolution.
With a PC chances are the only thing you'll notice is that everything's now smaller. If a program window was 800 pixels wide, with a higher density monitor it's still 800 pixels wide, but since each pixel is now smaller, that window's much smaller. You can adjust that in Windows, so everything's the same as it was, but then what's the point of higher pixel density? The moral of the story: when it comes to choosing a monitor often you should be more concerned with physical size than resolution. That's the opposite of what you'll sometimes read.
You want to make life easier on more mature eyes? Consider a 27" or larger display at 1080p or even 720p. WR once posted he was using a smaller HDTV, & that's perfectly fine, bearing in mind that you have to sit far enough away from the display to see the whole thing. One final note, I always thought that a 24" monitor was perfect -- I couldn't imagine wanting anything larger -- & then I moved to a 27" monitor, finding that it now bothers me using my wife's PC because that display's only 24".