Comment by pca2

I have used a one-handed keyboard for 20 years. My current set up is using

- A 25 key Macropad (really an external numpad) Something like this, for around $50 USD https://www.dhgate.com/product/25keys-macro-keyboard-kit-pro...

- The keyboard supports QMK, the customizable open source keyboard firmware

- I programmed my own layout using the Frogpad style layout others have mentioned. Its central feature is that it is what's known as a "chording keyboard" in which you hit multiple keys at the same time, like a piano chord, to trigger different letters.

- The reduced keys on the keyboard mean I can comfortably produce any character at normal speed with one hand without moving my wrist in a way that would cause RSI.

If you want more info or a copy of my QMK config let me know.