Might a “modular monolith” be the happy middle ground in the endless monolith or microservices decision? You may have to answer that question for yourself, but this post shares some good thoughts around designing a modular monolith:

When designing a modular monolith, it is all about breaking up the system into modules, and then combining those modules into a monolith for deployment.

It might be worth noting that finding what modules you will need, might not be as easy as you would think. They have to be as independent as possible. High-cohesion and low coupling is very important here, as all communication between the modules might end up being a cross network call, if you decide to break it into services in the future.

This means that all communication between modules need to well abstracted, and be either asynchronous, so that they can handle the call going across the network in the future, or use some form of messaging.