DeGoogle Yourself

I know there are already Gmail alternatives in the pinned post, Protonmail and Tutanota. I've experimented a bit with both of them, and both Tutanota or the free Protonmail are out of the question since I can't use them with Thunderbird, so I don't have a convenient way to keep all my mails stored in case my account gets deleted or I get locked out of it. And getting locked out of it, I already have once for Tutanota, right after making my account, for no reason, and it took me three days to get it back after sending a mail from another address.

Disroot seems good enough, at least for communication. But for making accounts for official stuff, I'm still a bit worried that I could lose access to my account before an important mail has been downloaded, or that I'd be unable to recover a password or contact some important service if something happens to my account, so I'm wondering whether I'd need something... "Bigger". A service that has less chance of going bankrupt and being discontinued, but without being google. I'l considering "laposte .net".

Any thoughts? Do you guys think I'm right, or do you think using more open-source and privacy friendly stuff for everything is completely safe?