Legally, I believe the concern needs to be about what you're riding on when "outside" the fence/guard rails while underway (faster than "no wake" speed?). Not sure if anything will meet those requirements.
Regarding lawn chairs, depending on the style, those can be pretty unstable if the boat is hit by a wave or wake from the side. Speaking from many years experience using them on our boats, which seldom have furniture ahead of the helm, I've seen plenty of people caught unaware and toppled onto the floor (no, not all were drinking, but some maybe). The most stable seat we've found are the plastic Adirondack style. They have a wide foot print and are nice and low to the ground. Have never seen one of those tip. They're comfortable for hours on end and all we ever use any more. Bonus is they stack nicely to get them out of the way when necessary.