I just used baby onesies put on backwards on ZoE after her spay. We never used a collar of any kind. (I do think a soft collar is a great investment though to have on-hand in your first-aid kit in case of emergency).
Here's how the onesie looked on in pic 1 and with her tail sticking through the middle snap that was left open, in pic 2.
__________________ (ZoE  )(Chelsea ) |