...also migrating AWAY from Fastmail (Australian) and TO an European provider sounds like a very bad idea - I'd kind of want both the US and the EU legally away from my coms at all costs (!)
While I agree in principle, I have to remind you (and to myself) that Australia is part of the Five Eyes: https://en.wikipedia.org/wiki/Five_Eyes
Fastmail runs exclusively of AWS in the US.
I looked into this, there are lots of people in forums discussing/ asking for EU based servers.
As EU citizen I at least got some influence into EU policy. A government far away doesn't even have to pretend to care about me.
Is it that different? Being Australia in alliances like "Five Eyes" I don't think you can keep your stuff away from the US at least when using Fastmail.
If you want both US & EU away from your data, I suppose you will have to consider things like Yandex Mail, which comes with its own set of problems too, of course :)