Interesting. I have always used their web app (even on mobile, i just use their pwa instead of the native app since the native app is missing obvious features), and I haven’t had any issues, but I can definitely understand the frustration if you want to use anything else. OP, keep that in mind if you’re thinking about Proton!
Just throwing in my two cents since I just went through this same ordeal: I use Proton, but be aware that you can only use a custom address if you pay for the premium plan which is not crazy cheap. I’ve been pretty happy with their premium plan so far, which includes premium features for mail, calendar, cloud drive, VPN, and password manager, but if I ever decide that I don’t want to keep paying for it, I can always transfer my custom domain to a different provider without needing to update my email.
As for the domain, I went with namecheap. I also have a pretty common name, so the good domains were taken and I had to settle for firstname@lastname.in but I think it’s still pretty easy to remember.
Related https://youtu.be/K1kkel0CECc?si=hjSjlpi64mjHJ5Jn