Moving away from ProtonMail I looked at several options. Changing email addresses everywhere when I change providers seemed so unflexible, so I've set up a #selfhosted @simplelogin instance and moved all my aliases there.
Right now my default mailbox points to @Tutanota but changing email providers is just changing the address of the default mailbox in my SL instance!
And I can even use PGP between SL and the mailbox, if there are add-ins or the provider supports it ootb.