Black Ugg boots

Black Uggs are missing a strap on each boot. They can be worn as is, but if they weren’t too tight, I might search out a solution. Waterproof. Leather, rubber, felt wool (I believe). Tag says size USA 9 and EU 40. I wear an EU 39 in Alegria and a 9.5 in most everything else, but these are too snug for me. I don't think I will ever find a pair of Uggs to fit me - my arch is too high.