I wear a 5-7, but usually a 6 1/2 US. For water equipment sometimes even size 4's are way too big. For me a Wave with neoprene socks was good. I currently have the smallest size Finis competitor, which is waaaay too big, but with 2 pairs of 2mm neoprene socks fits well so that may be an option. Also the monofins in the official monofin thread have monofin makers listed over in Europe, and they have much more customizable fins. Wider choice of sizes as well as hardness and other specs Plus they're cheaper than the overpriced Finis Competitor! If you're looking for a floppier fin, the Merfin has kids and adult sizes so I'm sure you could find a small enough size! Good luck!