I have a somewhat narrow foot and have a hard time with slip-on shoes or sandals. In a few of my slip-on pairs, they just have a wide piece that goes over the top of the foot, leaving the front/toes and the back open. But the wide “strap” over the shoe is too wide, so my foot slips out as I walk. Is there anything I can do to tighten it a bit? Because the whole shoe is open, I can’t stuff anything into the shoe.