Yeah, I thought of that too. I even have a couple of PS/2 optical mice. One works and one does not. So, again, I am left wondering which optical mice are compatible. Just because it includes PS/2 support, is no guarantee Cocolino will like it. The one that works was a random find in a junk pile and is missing feet. Not ideal to use that one.
Then there is the thought that if I have a USB optical mouse that is also PS/2 compatible, the optical resolution could be higher/smoother than an older PS/2-only optical mouse.
For $5 USD you can buy a new optical PS/2 mouse for your Cocolino via Amazon or eewBay.