Are there any options left at all to self host email?

You can absolutely set up SPF, DKIM, and DMARC for yourself, it's really not that hard if your difficulty reference point is self hosting email. I did it like 10 years ago and I don't think it has changed.

Self hosting is hard (which is why I just use Fastmail now), but it's not because of that.

Sure, I do it, and many others. Some people say it's hard, but I think it's much easier than it used to be, technically. You have projects like https://stalw.art which make it quite easy. Single binary setup which covers all functionality you need. Setting up SPF, DKIM and DMARC is also easy. The only thing that remains is IP reputation, but even then, I haven't had major issues. People seem to receive the few emails that I send.

Tonnes? I don't like to say 'just search for it', but seriously you'll get more out of that than a response here. Personally I use SES for the 'hard' bit, but there's loads of OSS if you want to self-host the actual receiving too. (Sending probably requires more time looking into getting a trustworthy static IP than software. Again, I bypass that by using SES, but that's technically only self-hosting storage & client.)