I’m not familiar with Hall effect switches - any recommendations on a keyboard for ergonomic use?

Hall Effect switches are a pretty recent (re)addition to the keyboard market, so it might be difficult to find an out of the box ergo keyboard with HE on them.

Most of them are on gaming keyboards due to the possibility of getting super small actuation and rebound windows for faster input.

So you'd probably need to do some DIY (there are switches available for purchase, might have to do more reasearch).