I am a fan of Standard Notes, but crypt.ee is also solid as far as I know.
Both Proton and Tuta are great choices. Of the two, I prefer Proton simply because Tuta’s UI makes my head implode.
But for my every day, general email usage, I have gone with Posteo.de. They are pretty cool and work seamlessly with any email client of your choice (no need for Bridge, or the like).
If you actually decide to give it a try at some point, I would love to hear about your experience as I do not have hands-on experience with cryptee myself.
Do be aware that they use progressive web apps (so there is no “cryptee app” in App Store or Google Play). But this is actually an active choice by them to enhance security.
If you want to take a longer deep dive into the mind of their CEO, Techlore interviewed him fairly recently.
The interview ran so long that they had to make it a two parter:
https://youtu.be/JsWCSHYY9FU?feature=shared
https://youtu.be/xE-YXAnOTeQ?feature=shared