Cheers for the tips. Had a look at the Aldi ones. Was not sure about the fit on them. The Prendas ones are looking like the way to go.
I had the same problem with Aldi - size too small to fit over the shoe. But because they're made of fabric, I got one size smaller and wear them inside my shoe as a kind of second sock - over the sock, but under the shoe.
They work really well.