Thanks everyone for the replies, it's been interesting to read about other peoples' experiences. I'm happy with the changes I've made so far (DDG, Apple Maps, FF on Windows), but my main sticking point is the email issue. As mentioned previously, I've looked at something like Proton Mail, possibly with a custom domain, but there's a couple of things making me hesitate:
1) On my iPad and iPhone, I currently use Apple's mail app, as I don't have that many requirements, and it works for what I do. However, if I went with Proton Mail, I'd need to either use the web interface or use their dedicated app. I have to admit I haven't tried it yet, as I haven't needed to because I haven't made the full switch. I think I need to download it and give it a try. I'm less fussed about the desktop side as I usually use the web interface with Gmail anyway (I'd need their Bridge app to use a desktop mail app).
2) I'd love to have a custom domain, but I was thinking about using my family name, but that seems to be taken already with the better top level domains. Also, people often have trouble with spelling my surname anyway, so using it as a domain name would just cause more trouble!
Also, related to (1) above, why is the iCloud email web interface so poor? I guess they expect people to use an app to access it, but still...