Asking for a GIT workflow recommendation

Hi everyone, I have a project that I'm doing for a friend, but later I asked him if I can use the project for reselling it and making it open source with the intention to have two projects that will be evolving differently, primarily the front-end- and logos.

However the private project still have small issues here and there, so I want to make bugfixes in any project and share it when it doesn't change the purpose of each project.

I was thinking in having two different directories in my computer and both of them having two remotes so I can make pull requests to the not origin remote and the origin one. I tried that, but after some features I found it a little bit messy. I will be the only developer for a while so there is no need of making the workflow the simpler but I think I'm over-engineering the workflow so I wanna know if anyone has worked with a similar approach or if you recommend just having two branches for now. Or any other suggestion.

Thanks