stb, gb, zpl, sokol, and many others are good bases. EASTL as well (if you like the heavy C++ features).

Personally think its a good thing to slowly resolve what you grab from them manually for a long-term codebase (even for prototyping). If you have dispiline with docs and how you format the code uptake of slightly diff impl should be a non-issue.

Recently got my staged metaprogramming project for C/C++ generating a C11 version. Been also inspired by the sokol libraries to setup a context struct so everything can be configured from there (allocators, viewing state, etc).
Goal now is to improve error handling, code path simplification, and just using it more on some projects.
&gencpp
https://github.com/Ed94/gencpp

Been working on this staged metaprogramming library for C++, its my first project taking a handmade approach.

All code is either from scratch or derived from the zpl-c library. The convention used is an "orthodox cpp" subset.

Got it to the point where the library could construct and serialize itself.

A C library version is also in progress.
https://handmade.network/p/416/gencpp/