Alternative to Gmail as a backup email address?

I have degoogled myself when it comes to email, running self-hosted email & calendar (not my own server). Did it two years ago, and up to now it has worked very well. I don't miss anything from Gmail and have all the features it offered, plus some extra ones (like deleting email attachments via an email client – Gmail never deleted them, just archived them).

It's good, however, always to have a backup email address that's not connected with your hosting service. Up to now I've been using Gmail for that, but in view of recent developments, I just want to ditch the whole Google business.

I've seen that many people use Protonmail for this, and that's what I'm considering. I'd like to hear about more possibilities and experiences though. Maybe there's another provider that's friendlier or more consumer/internet-freedom oriented?