While I was rummaging around the cheaper end of Ebay (as one does), I found a 1280 by 1024 LCD monitor for only £25. And it does HDMI!
I thought about the little three inch screen I currently have my alerts on, and I thought, this is what I need.
It arrived today, and I have it in action now.
To use it, I set the framebuffer
And the HDMI mode
The information displayed comes from my external temperature sensor, my mail server, and the Pi's clock.
I'm using Imagemagick to create the bmp file with the information, Then I convert that to a framebuffer format using ffmpeg. I have no idea why I needed to do that, but I couldn't see how to make Imagemagick create framebuffer formats. Then I copy the file to /dev/fb0.
The alerts thing goes yellow if it's looking bad, and red if it's very bad. Red means that a server is definitely playing up, and needs to be checked out.