Step 1 : go with the one company that's known worldwide for abusive & permanent bans with no recourse.
This post is a bit too generic, but it's true that using your own domain for mailing is the best solution to avoid getting locked out. Although you need to pick a good registrar, too...
The saddest thing though is that in some ways Gmail is harder to hack into than some registrars. I remember a postmortem write-up from a guy who had his personal domain easily hijacked by social engineering someone at the domain registrar, which then served as the foothold of a larger identity theft attack against him. Google, by virtue of simply not even doing customer service, is much harder to social engineer, so the author of that piece pointed out that ironically if he'd put more of his eggs in the GOOG basket, he'd have been safer.
This seems like a potential rabbit hole.
Use a different domain with your registrar than the domain you’re registering. Same thing with DNS host. Do you have two domains with two registrars and two DNS hosts? Presumably if either one gets compromised, the control of one domain could be used to gain control of the other. And you’ve quadrupled your attack surface by having two domains with two registrars and two DNS providers.
I don’t disagree with you, but I also don’t know a robust solution for this (happy to hear one, if you have it).