I honestly wasn't joking at all. It's something I've thought of off-and-on over the years.
I could see how a trust would be better, though, in the US at least, I think a corp / LLC might be more flexible. And here, especially if the corp is formed in a few rules state like Nevada or Delaware, the paperwork isn't too terrible for small organizations.
But it's an expensive option given all the paperwork (and taxes) you'd have to file at least once a year.
In the UK, you'd probably be better off incorporating as a trust - perhaps even a charitable trust, if you can find a good enough cover story.
And you may think you're joking, but a lot of families set up financial trusts for their assets for exactly these reasons.
It would be unusual for a trust to include non-married partners, but I don't see why it would be impossible.