One problem I can see with putting something like a pillow case ove the dogs head and attaching it to the collar is that it would cover the eyes. Then you would have to carry the dog. That is why I suggested the muzzle as a base for the mask.

Speaking of collars I would recommend rather than the around the neck collar go with the kind that includes a chest strap. If you have any pet oon a leash and it gets away the leash can get hung up. If they have all four on the ground there is time. But ic they get hung up going over something there is little time before air runs out. The chest strap would help support the weight rather than just the neck.