Quite simple, key the pokemon moves 1-4 so we can use one hand on one method of controls instead of having to use the keys and mouse/ trackpad.

Thats already working as you explained.

it already works, you can also change the keybinds of them in the settings, you can use the buttons for everything:
on the main selection, you can use 1-4 (or whatever keybind you associated it with) to select "Fight; Pokemon; Items; Run"

in the next selection, if you click fight, 1-4 will select moves, ordered top down, so 1 is the top move, and 4 the bottom move, and there is a "Go Back" button, i don't remember the default but i think it's escape. If you select "Pokemon" you can use 1-6 to select which one you want, 1 being the top left, 2 the top right, and 6 the bottom right. Items i don't know how works, but you can use 1-6 and maybe more, i haven't tried, to select stuff like pokeballs (using 1). and finally, run, which is self explanatory.