nostr:npub1j46f9va5qdrmamcwmncew7g8mwekgma386dhws6k04fsnlkqpcpsj23gm7 Have you had a look at the MessagEase keyboard?

I've found that swiping left/right on the spacebar to move one character at a time combined with swiping up on the backspace giving me a delete key (inverse of backspace) means that I can be imprecise with my finger taps but still very quickly do edits.

Additionally swipe-and-return on backspace deletes a whole word, which is very nice.