Respiratory facemask with inlet and outlet valves for physiology experiments

Having tried the AD Instruments facemask, which we bought at £665 including two masks and the necessary valves (https://www.adinstruments.com/products/face-masks-and-kits) we identified several inadequacies in the design. First, it is heavy (284g), so it has a tendency to slip down the face when sweating a lot. Second, the design is very uncomfortable (at least in my view) during prolonged wearing as the mouth and nose compartments are separated by a ridge which digs into my upper lip. Third, I