Unless you have a set of objectives that are very different from what I consider "as secure as e-mail gets", please consider GSuite and not Protonmail. (I don't speak for 'tptacek, but I'm pretty sure he'd agree.)
As a corollary: if you really care, use Signal for stuff you can't say over e-mail. Whatsapp's fine too. But they solve a very different security problem than the one you need e-mail to solve, which is mostly "don't leak my emails" and also "don't reset my password for attackers who ask nicely".
As a corollary: if you really care, use Signal for stuff you can't say over e-mail. Whatsapp's fine too. But they solve a very different security problem than the one you need e-mail to solve, which is mostly "don't leak my emails" and also "don't reset my password for attackers who ask nicely".