Why not something p2p and encrypted? https://peerloomllc.com/pearpetal/ No servers, no problem. You fear losing your device? I'm sure you have more than one, any additional one you have is a fully functional backup.

The technology it is built on is extremely cool. http://pears.com/

Or better yet. Why trust this one (even though the source is on github)? You can just ask your AI agent to build you your custom one on the basis of this technology.