Thunderbird.
Yah, TBird is best. Works for all flavors of M$. You might have to work thru local WWW supplier (e.g., AT&T, etc) to set up a secure password when TBird starts up. But, that is no big deal. Basically, you set up a password with the WWW supplier and then enter it into TBird to use without any further intervention from you.
As to Linux, TBird works there, too. But, I would not dump M$ and go to any Linux flavor just to get a better eMail application. Waaaay too much trouble. And I dual boot several PC’s with MS and Linux.
Re transitioning to Thunderbird, I assume you would get a new email address with @Thunderbird.com ...?