You’re right to be reluctant to apply everything by hand. K3s has a built-in feature that watches a directory and applies the manifests automatically: docs.k3s.io/installation/packaged-components

This can be used to install Helm charts in a declarative way as well: docs.k3s.io/helm

If you want to keep your solution agnostic to the kubernetes environment, I would recommend that you try ArgoCD (or FluxCD, but I never tried it so YMMV).