That requires 2 fingers, which is too complicated when I'm deep into reading something.

But TBH I've previously remapped the shift keys as extra page up, since when pressed and released they do nothing which is a waste for such a big key that's so easy to reach!

Unfortunately, that's not standard everywhere. I've found that some CLI applications go the route of space and B being the pager buttons, but I haven't found keybinds for paging in a bare TTY.