How big are these "micro" services that you're decomposing? And what criteria do you use to differentiate a service from a microservice?

Functional decomposition makes sense applied to service-oriented architecture (SOA), where domain services encapsulate the functionality and data belonging to a given business domain.

Microservices typically result either from this kind decomposition (domain service -> business entity microservices) or from "greenfield" design and development.

In my opinion, there shouldn't be enough in a microservice to warrant further decomposition.