For a solo dev, it's not difficult. C++ is nearly a superset of C. You don't have to adopt all of C++ to start using it and to get immediate benefits from it (for example, unique_ptr, shared_ptr, and vector would all be things that I think any C dev would really appreciate).

A reason I can think of to not move to C++ is that it is a vast language and, if you are working on a team, it can be easy for team members ultimately forcing the whole team to become an expert in C++ simply because they all will be familiar with a different set of C++ features.

But for a solo dev? No reason not to use it, IMO. It's got a much nicer standard library with a rich set of datastructures that just make it easier to write correct code even if you keep a C style for everything.