I bought The Attico Vitto boots in 37, they fit perfectly in the toe box and across the top of my foot but my heel slips a bit in them when I walk. I'm afraid if I go 1/2 size down (to get my heel closer to the back) the toe box will be too tight. I'm desperate to keep these but my narrow heels are making me 2nd guess the sizing. any remedies for slipping heels?