I've been using UK 3 size for a while now. But when buying a new pair, the size 3 feels a bit pinched on my feet. Not sure if its due to the material or fit since its a different brand. But the size 4 feels like its a bit big on one of my foot, I can probably fit in one finger at the back.The seller told me that the smaller size will stretch but I'm not sure if it will really stretch enough? The pinching is a bit painful. Or would getting an insole or something make the size 4 fit well?