I have a confession to make - we had both Star and Ruby spayed shortly before they turned six months old. We didn't use the collar or a onesie on either one, because neither of them ever bothered their stitches. Actually, their stitches were internal, with the incision "glued" shut. My vet says I am bad, bad, bad.
I did have a reason, though - one of our cats had to have surgery several years ago after he ate some ribbon (our house is now baby-proofed for this guy; he goes nuts over any string, ribbon, etc). He had to wear the collar for a really long time, and it caused a sore on his neck, and eventually a small bald spot. That's why I tried going with nothing for the girls.
But as they say, don't try this at home...
Barb, activity director for Star (tri-color girl) and Ruby (Blenheim girl)