remembered that you were looking for peripherals or things to 3d print up, and I've been having good hand experiences with this lately, so I figured that I'd share
recently whilst watching some youtubers discussing their disabilities (missing hands,etc) I saw one of them suddenly bring up a pair of devices called the Azeron cyro and Cyborg which caught my attention.
they are basically 3d printed mouse and keyboard replacements made in Latvia that are designed around making it so you can do the absolute most with each hand possible, basically about maximizing efficiency without being uncomfortable, confusing or cumbersome to use.
the cyborg focuses on giving you 26 keys on one hand plus a thumbstick, whilst the cyro gives you 22 keys inside of an ergonomic well, a thumbstick, and a joystick selector within the framework of a light vertical mouse.
as someone who suffers intense hand strain from using keyboards and mice and wants a replacement for both pretty badly, I was pretty interested so I bought a left handed cyro (i'm right handed) to combine with my more dominant peripherals and have been testing it with a few fps's lately and have found it to be one of the best devices I've used
Basically, it does what it says on the box; it gives you a large amount of inputs per each finger, arranges them ergonomically in a way that makes it easy to remember the layout via touch but doesn't cause any notable strain
I cannot emphasize the ergonomic aspect of them enough; I'm playing with this in one hand, and an empty trackball in my right, just for clicking, and the trackball manages to give me notably more strain, despite it being a device I already use to reduce strain
basically, because of how the keys are arranged in a well, my fingers barely have to move at all to hit most of them
both devices come with free software that allow you to program the inputs to do any amount of things, so for instance, if you don't like thumbsticks, you can instead program them to function as selectors and use them to switch between profiles and programs to further increase what you can do with them
I'm sure that if Ross were to look at them, he'd have plenty of issues with them, or find bits of em tacky, but if you want ideas for how to go about making a versatile mouse, I would strongly recommend looking at these, as they are genuinely one of the better peripherals I've used
https://store.azeron.eu/azeron-keypads#keypad=cyborg