I’ve seen a ton of XKCD webcomics without myself realizing it but this popular webcomic is certainly not only for reading, you can also make one of these XKCD pillows yourself.
Although I resort to quick and easy method of ironing pieces of heat-transfer paper, for this project you will probably need to resort to some serious screen printing, which is probably a great skill to learn on making T-shirts too.
Here’s an excerpt of the author’s screen printing method:
Take your stencils and remove the bottom pieces (bottom pieces = non-printed pieces) of paper from all of them (you’ll probably want to either do the words or the outline first). Line them up how you want them on the material and iron them to it. I would probably do the outline first, since then you know more where you want to place the words.
Use a paintbrush (those foam ones work best) and put paint wherever it’s supposed to be.
Let it dry for a while and remove the stencil. Then repeat with the other stencil you’re using.