Seriously, once you make the move to your new Operating System, stay there. Yes, you will have problems that arise. But don't backslide to using the familiar. Work your way past the bottleneck. You may need to Google a whole bunch of stuff that you do not realise that you don't know about. That then becomes a way to move forward.
I would give this same advice to a Linux user like myself moving across to Windows.
When I moved from MSDOS to UNIX back in 1991, there was no Google. So it was difficult. I could work my way around MSDOS with no hassles at all, but the simplest things, almost, in UNIX had me floored quite often. But persistence and trial-and-error experimentation paid off.
Probably what I'm trying to say is that you may need to find your own path to which email client is best for you. Recommendations for an email client may give you somewhere to start from, but they will never be as good as where your own experience and your own requirements will lead you.
Forget what you did in Windows, that won't really help you in Linux. It may even hold you back at times due to the different mindset and different attitudes of Linux/UNIX developers and users.
Good luck!
(And don't worry about about having gigabytes of emails hanging around. I have gigabytes of programming stuff lying around on my system, even source-code files from back in the 1980s.)
Thunderbird has a client that runs on Windows. You can try before you buy.