Yeah, don't use Proton, they're several types of shady. If you can figure out running Matrix, that's better. Email isn't built for security, don't treat it as if it was. Use PGP on the body if you want, but the metadata will still be very talkative.

The Grugq has complementary advice which arguably is more important, regarding foundational principles, personas and so on:

https://www.youtube.com/watch?v=L3j1AhS0iKI

https://www.youtube.com/watch?v=3w7E4Hhtubw (there's a bit of presentation and ceremony before they get into the relevant parts)