ThermalTake is selling a fairly small Bluetooth mouse. It seems pretty small when you look at the pictures. I like the fact that it has a physical on/off switch so that makes it good for traveling.
I use my TR a little differently than most of the others here. My TR is my road/commuting machine not my main home machine, so I don’t usually have the space to use a mouse with it. The touchpad is small, but works for me. On my desktop, I use a (wired) Logitech MX500.