Zin Alloy Enamelled Cow Heads, Sized 22mm x 21mm. Gold Plated, Multicoloured.
With really flat tesserae like these, I usually glue something to the back of them. Usually a large seed bead, or even just a blob of thinset. This is to give it some height, so it doesn't get lost in your mosaic. Alternatively, these kind of tesserae can be glued on after a piece has been grouted and cleaned.
Don't be limited by your materials, play with your tess-array.