I'll offer a suggestion. I won't claim that it worked perfectly.
I was going to be on foot in Alaska, and there would be some wide stream crossings that were almost knee-deep. The water was to be very cold. The stream bottoms were seldom sandy, sometimes with rounded pebbles, and sometimes with jagged rocks. This is BPL, right? So, I wanted something that would likely keep me drier and warmer than just walking through the cold water, but I didn't want the weight of fisherman's waders.
I got two clear plastic bags that were long and narrow. They were long enough to go from my feet up past my knees to mid-thigh. The width was sufficient for my stocking feet to fit in, but they would get snug around my thighs. I had some extra boot insoles, and these got taped onto the bottom as puncture protection. I had some rubber bands that fit around the tops to hold them onto my thighs. This rig was lightweight, durable enough for three or four wide stream crossings, and cheap.