I haven’t read the book myself, but I’ve heard that “World War Z” by Max Brooks deals with this topic alot. Not so much in the movie - obviously.

I honestly don’t know which would be the ideal form of governance but I think I slightly lean towards groups choosing a leader which would then effectively become a dictator of sort. Ideally there would be many groups though so if you don’t agree with the actions of one, you could join another. I have a feeling that democracy might not be the best choice especially initially. Life in a post apocalyptic world mandates that very difficult decisions will have to be made.