It seems that everytime I have a big fish in swift currents, I eventually lose my footing and fall into the water. Usually it's only knee or bum deep, but one day something's gonna happen. I know my rod floats, so it will eventually get picked up by somebody. But what about me? lol. After the first spill, I decided I wanted a bit of assurance, for that eventual what-if situation.
When wearing my chest waders, I use a mustang belt-type inflatable PFD for my wading belt. It does double-duty as a wading belt, and as a pfd if needed. It's totally discreet, and doesn't get in the way of casting, fighting fish, etc. 35 lbs of floatation should be plenty, even if there's 20lbs of water in my waders, because most foam-type pfds have only 15lbs floatation.
It requires you to jerk-to-inflate, and then pull it over your head.
They're about $150. About the price of a semi-decent reel. But enough to save one's life.