I've cancelled my subscription yesterday, conveniently it was about to renew at the end of the week, so I have a few days to migrate from Proton, here's what I'm thinking of, but I'd love to hear what other people are switching to
I don't have a known good resource, but you should look into K3S. https://docs.k3s.io/
The documentation is very dense, I fear. I would probably go hit youtube search for "k3s cluster" and find a beginner that doesn't annoy you too badly.
The general path you'll have to do is:
Translate Configuration: Convert your docker-compose.yml settings into Kubernetes YAML manifests
Install k3s
Map Storage and Secrets. Replace local Docker volumes with PersistentVolumeClaims (PVCs) and .env files with Kubernetes Secrets and ConfigMaps.
Deploy and Verify: Apply your manifests using kubectl apply and verify routing through the built-in Traefik ingress.
Then you can install and add a new node.
depending on how you set it up, it'll move the containers around for you automatically.
Note: all your k3s nodes need to be very close network wise. you can dump one at a friends house and make a cool geo-diverse setup, they need REALLY low latency