https://linkerd.io/ is a much lighter-weight alternative but you do still get some of the fancy things like mtls without needing any manual configuration. Install it, label your namespaces, and let it do it's thing!
Also I'm worried about its pervasiveness. Is it possible to enable those side-cars only on selected pods?
It's not possible to disable mtls with meshed services, no configuration option for this particular feature.
There's no pervasiveness with linkerd, one need to add `linkerd.io/inject: enabled` annotation to the target service and restart deployment.