I play guitar and banjo with reattached fingers. The injury happened 30 years ago and the soft tissue damage to my hand was significant and remains so today. I used an autoharp for physical therapy after reconstruction surgery and hours of gross motor therapy on my left hand. This was all well known to me. I had a similar surgery and therapy on my right wrist 5 years to the day before. So I had been through this twice.

I was able to play when all this was done. I couldn't play the same as before but I could play.

In my professional life working with people with disabilities I often suggested Autoharps and lap dulcimers as therapy instruments. I would with you based on your description. Autoharps can be played in many styles. Check out videos of Kilby Snow. I might also suggest a Hawaiian guitar strung for left hand and tuned to an open chord.

Good luck.

Don