For daily to-dos a generic 58mm Chinese ones is probably enough. For pen and paper stuff I highly recommend going with anything 80mm, as 58mm can be too narrow...
Search "58mm usb thermal receipt printer esc/pos" on Amazon and you will find various generic models
Isn't your problem more about Color quantization than about dithering? If you have big character cells like in a terminal dithering won't help you much. For each cell you want to find the best shaped cell and a foreground and background colour that are the closest to a colour from the supported palette.
But maybe I didn't understand your real problem yet
Sorry for the confusion. The use-case is a little difference because the goal is to display the image as close to the original as possible with the limitation of only being able to use a forground color, background color and character per cell. The character is selected based on it's shape just like in the article. So if you get rid of the colors in Chafa you end up with something similar to the article. That's what I wanted to say :D
In the "Image to Terminal character" space this is also a known solution. Map characters to their shape and then pick the one with the lowest diff to the real chunk in the image. If you consider that you have a foreground and a background colour you can get a pretty close image in the terminal :D
Search "58mm usb thermal receipt printer esc/pos" on Amazon and you will find various generic models