I've been testing migadu[0] since a ShowHN about it a few weeks ago. So far the service is awesome! It maches all of your criteria, plus, for a flat fee (it depends on outbound emails/day actually), you get:

* unlimited domains, mailboxes, storage space

* a very well-thought and honest service and UX ( I encourage you to read their "benefits" and "drawbacks" pages)

* a very responsive and helpful customer support

* hosting in a privacy minded country

0: https://www.migadu.com/en/index.html