rouille (https://github.com/tomaka/rouille) is a nice micro-framework that I've enjoyed using at work. Simple, sync, and no plans for async. We've similarly been wanting a framework for the reasons you outlined above.

Rouille has been unmaintained for a while and had some RustSec issues last time I checked, but there has recently been new activity/releases on the repo . Fingers crossed for long term support.