In our case, we have a codebase that involves two submodules: one for persistence and one for python based management of internal git repos. Both of these are standalone applications and can run on their own. They are then used in a parent repo which represents the overarching architecture, which calls into the submodules.

The advantage of this is, that work can be done by devs on the individual modules without much knowledge of the overarching architecture, nor strong code ties into it.

Right now our persistence is done with SQL, but we could swap it with anything else, e.g. mongo, and the parent codebase wouldn't notice a thing since the submodule only returns well defined python objects.

Of course, this comes at the cost of higher number of commits as you mentioned. But in my opinion these are still cheap because they only affect trivial quantity and not brain-demanding quality.