I just looked into turtlecoin, seems like a maintained fork of cryptonote. Let's see how it goes. 

I know there is a tutorial on how to fork Bitcoin from 2018, but is there any easier/simpler coin to fork? Such a big codebase like Bitcoin's seems too hard to maintain and work on as a single person or even a small team.

There used to be https://cryptonotestarter.org/ which was made with the purpose of being easy to fork but it's abandoned and dosn't seem to work on newer Linux versions.

Do you know or any other guides or coins easy to fork? 

Any simpler coin to fork? I heard Bitcoin used to have like 3000 lines of code, while now it has 100k+
A simpler coin with less code should be easier to fork and work on top of.