A couple of years ago, I was in an incident that reduced the strength in my left shoulder. I’ve been waiting for an operation to restore the function to that shoulder, but we were warned the post-operative recovery period would be several months. So I started looking for keyboard options...
I made a similar attempt at a one-handed keyboard using half of a BFO-9000. Never managed to get above 20wpm for the couple months I used it, which was the same speed as my one-handed hunt-and-peck on a qwerty keyboard. The important thing is to put the most used keys on the top layer. Having control and shift mapped to foot pedals was also useful.