I have always worn a size 9/39. I think the addition of 1/2 inch more material to the height of the heel would fix the problem. LOVE THIS PRODUCT! Please consider offering your high tide in green. Fit Flop makes some of the best soles. I have only been wearing this for a week but I love it! Most of the time the earpiece on these types of headsets really put pressure on my ear and over time my ear gets sore. I could not put my feet in them! In another review, the person mentioned that the battery only lasts half a day and gets very hot. My three year old also helped.