I have used Fastmail, and it is good. Currently I'm using my own domain on iCloud+, as I'm already paying Apple for the right to do so. But that's the good thing about owning my own domain...I can take it with me.
+1 for Fastmail. Great service
protonmail is better, plus their plans have VPN and file storage.
Protonmail is very expensive for what it is. I don't care about their privacy (it's email) and I don't need anything but an email service that can support 3+ domains.