i just purchased a beautiful sheepskin footmuff from John Lewis. It says it fits any 5 point harness and it does, kind of. The straps fit through fine however I don't know how to attach it to the buggy. There are 2 black strings on either side at the top, but what do they tie to? DS constantly just slides down if the buggy is seated upright and screams in pain as the harness cuts into him. So please help!