Yeah, I’ve used Okular for a while now on my desktop and it’s generally been fine (definitly far better than GNOME’s pdf reader), but I’ve found it’s text insertion routine to be a bit finicky (although it’s possible I may have missed a better way to do it), and I don’t think it’ll work well on a tablet. I will still give it a shot though once I can!

Proton has a great free tier that may work well for you. I’ve used them for a while now and it’s been great. They have what is probably the most feature-complete private email service out there (unless I’m forgetting something). The main nitpick I have with them is how little they focus on Linux, but that applies more for their other services than email.