I decided to set up a URL shortener on my short domain, aaronpk.com, thanks to some recent discussion in the IndieWeb chat.
I found an open source project that is basically exactly what I would have built if I had built my own: https://polrproject.org/
The installation wasn't seamless, but I'm familiar enough with the tech it's built on so I managed to get it set up. I also made one modification to it, which is that if you type in a short URL that doesn't exist, it redirects to the same path on aaronparecki.com, so that all my regular pages now automatically have a short URL.
This is definitely a lot nicer than my previous solution of adding URLs to a text file.