When I was in Junior school (many moons ago) we made an oven cloth and our teacher got us to use an old matted up knitted jumper (100% wool) for the fill, we used cotton fabric one side and plain sacking/hessian on the other. To this day I use the same method to make my oven cloths and it works well, easy to sew through and cheap. Wool does not burn like cotton does and if thick enough, keeps the heat out.
Gal