I started this project in January, and finally found the buttons I wanted (via maman) in March, and got the final 10 I needed in May.
I have decided not to do the star decorations now. Partly because I lost my enthusiasm, and partly because the people I was mainly planning them for were TAs and teachers at my old job, and, well, I’m not there now.
I used up 62g of DK yarn stash, and bought £5 of buttons, so they have worked out at 40p a decoration (minus labour of course!). I am really pleased with them.