This is a great question that I am ill-equipped to answer! I have never gotten into solo gaming, but I have run a lot of duet games (one GM and one player) and I tend to give the player one NPC ally and one pet so that combat is balanced a little more in their favor.
Thanks for your kind answers in both threads! I've been trying into solo role play and i've been enjoying it. I might try working out the rules for solo play with your rules as a hack. I was also wondering if I could use your rules as a base to create other games, such as sci-fi settings, post-apocalyptic, etc, changing things like characters, backgrounds and enemies but keeping the core rules. Creating and publishing such a game would be possible (with proper credit of course)?