https://willfennel.com/posts/2022/10/26/cheap-ergonomic-keyb...
I keep my hands at shoulder-width and put them on the desk in a natural-feeling position. Wherever they land, that's where I put the keyboards.
Not sure if there is a better appraoch to place them in the best ergonomic position, but my wrist injury has gotten much better lately. That may just be a coincidence, but it feels like it's at least safe to say what I'm doing isn't making the injury worse.
I experimented with double keyboards and thought it required the modifier key to be used on the same keyboard as the other keystroke, which basically raised the bar too high for me.
So I can just do left-shift on the left keyboard, any right-side letter on the right keyboard, and it will be uppercase. Same with ctrl/alt, etc.
I can't promise you won't run into something that doesn't work, but I haven't found such a thing. On macOS my Karabiner keybindings also work without needing modifications to the config or whatever.
These tend to be location specific but try to find regional resellers of the PCBs.
Also worth checking out r/mechmarket, i.e. https://redd.it/wvf9dz