There’s probably no provider, paid or otherwise that you can be guaranteed to be safe with because they all rely on automated systems that can make mistakes. I would say you have more chance for active support if you go with a paid service like Proton though.
Apart from that, redundancy makes sense - don’t rely on a single email provider/service but have several independent email identities with your mail synced across them. This goes for associated data too - the worst part of having your account locked is losing access to your cloud-stored contacts, files, etc.
I would say that there is 3 important points to your question:
1: Use your own domain, this allows you to somewhat easily move providers.
2: Offline backup of your email. Keep a offline backup of you email, it could just be a desktop client checking email.
3: A paid provider with support, so you can get to talk to someone.
I personally think icloud is a option. Fastmail or hey.com could also be.
Apart from that, redundancy makes sense - don’t rely on a single email provider/service but have several independent email identities with your mail synced across them. This goes for associated data too - the worst part of having your account locked is losing access to your cloud-stored contacts, files, etc.