I use posteo, which satisfies the suggested requirements of being relatively cheap and the domain does not belong to me.

However, doesn't this allow a sibling to the described threat model? If posteo go bust, their domain could be claimed by someone else. Then, even if I change email providers, senders who haven't updated their address books will keep sending email to my old posteo address.

I think the points in the linked post are interesting and worth thinking about, but I don't think the answer is never use your own domain for email. Instead, maybe, just think twice, and have an answer ready to the question of what happens to your email if the domain name is lost.