My suggestion is, get yourself a domain with email included (I know a few european providers that I tested personally but I bet most of them include a mail service, even if it isnt advertised in the product page), can be had for as cheap as 6€/year. Test it out see if it’s enough and it works with third party email clients that you like.

Then later you can also purchase a dedicated mail service on top (but separately) of your domain, starting from 1€/month usually; the advantage to just the barebone approach is a nicer dedicated web interface, apps, support, etc. But it’s optional.

I’m wary instead of these all-in-one hefty and pricy (for personal use) services like Proton, do we really need all this interoperability between a drive storage and email and calendar? I think that’s the job of the operating system. Is copy-pasting a link to a different app really that inconvenient?