Some states require float tubers to either wear a life jacket/preserver/PFD or to have one "on board" while on the water. In any case, Wilderness Lite recommends you WEAR a US Coast Guard/FAA approved life preserver. Check your states regulations, which could require a USCG, rather than FAA, approved life preserver when using a float tube.
FOAM PFD
One alternative that is USCG approved is the Cabelas/Bass Pro lightweight foam life preserver with 3 nylon straps and side opening plastic buckles. It weighs just 15.0 ozs. This life preserver is adjustable and comfortable. Several of our Wilderness Lite team have used an earlier model of this PFD for several years. It can double as a sleeping pad or seat cushion in camp, and it is very reasonably priced. The disadvantage, it is quite bulky. It takes extra room inside (not recommended) or strapped on the outside (best approach) of your backpack when hiking.
https://www.cabelas.com/p/bass-pro-shops-recreational-life-jacket-for-adults-101596748
CO2 INFLATABLE PFD
There are several makes, models, and price points for "manual" and/or "automatic" PFD's inflated with an attached CO2 cartridge. They are comparatively expensive. Some of these also have oral inflation tubes to be filled by lung power. The oral inflation tube is advantageous as a backup in case of CO2 cartridge malfunction, and--as described below--reliance on oral inflation instead of CO2 can significantly reduce weight of your PFD for your hike. Manual (pull the handle to puncture the CO2 cartridge to inflate the PFD) and/or oral inflation, rather than auto--which inflate when becoming wet, are the best options when float tubing. Auto inflated PFD's may accidentally inflate if they get wet from rain or the very likely occasional splash in a float tube on the water.
AIRLINE STYLE PFD
A much lighter--but more expensive than the Cabelas foam PFD--is the Switlik airline style FAA approved inflatable life jacket. It is FAA but NOT USCG approved, which may or may not meet the regulations in the state where you are ultralight float tube fishing.
https://switlik.com/collections/airline-style-life-vests/products/av200-pax-vest?variant=268427702
It weighs 13.9 oz when equipped with the CO2 cartridge and a water activated light. Both can be removed and the life preserver quickly and easily inflated in a few breaths using the oral inflation tube. Removing the CO2 cartridge and light reduces the weight to just 7.2 ozs making it a great alternative when backpacking long distances. It packs so small it fits in the custom mesh stuff sack included with all Wilderness Lite float tubes together with your Backpacker Pro, Ice-Out inflatable seat, and double action inflation pump.