I bought Odie two Susan Lanci step-in harnesses, and they're too big. I was so upset when I tried them on her and they didn't fit, especially because her harness is getting so gross and these are gorgeous! I'm definitely buying the same style again, just a smaller size.
I have two XS/S up for grabs, in "Amethyst" and "Sunshine Drops". The XS/S fits a chest size of 11 1/2" - 13". However, when I measure Odie, her chest size is approximately just under 12.5", so I think these fit a bit big. I'd like $60 for both, plus shipping (which shouldn't be much because these are tiny).