After hunting around for DD's school shoes, finding something to keep her happy & the school, we found a pair of school shoes at last. However, dd appears to be a 5 1/2 - 6 & these shoes are a 6 so they slip a bit as she's walking. I have got some insoles for her, but could do with some heel grips too, bearing in mind she won't be wearing socks, which heel grips would be best?