I've decided on a bad leg wound, since the long-term damage from that would be particularly aggravating for this character
I may be preaching to the choir here, but don't forget the dangers of infection. As you're writing in the era before anti-biotics, surviving the initial damage from the wound was only the first battle. Even if a medic in your group is satisfied that the wound is not immediately fatal, they may likely worry about the prospect of gangrene if not properly treated.