You literally just set up a Mastodon server and only have a single user. That's what I do, and as far as I know it's the only solution.
A "lite" version of Mastodon that dispensed with all of the complexity involved with managing multiple accounts and was optimized for a single user might be nice but with a hosted account you're paying for data storage (which Mastodon seems horribly inefficient with) so in practice that extra complexity is moot.
Right, my point is, someone should stand up a service, like Blogger did for blogs, which were also trivial for people like us to set up and run on our own.
The thing there is it destroys the objection people have about having to find and fit in with a particular Mastodon server community.
It also makes Mastodon look more like the original blogosphere and less like Twitter, which is a good thing.
A "lite" version of Mastodon that dispensed with all of the complexity involved with managing multiple accounts and was optimized for a single user might be nice but with a hosted account you're paying for data storage (which Mastodon seems horribly inefficient with) so in practice that extra complexity is moot.