Actually I think they would feel turbulence worse than had they simply been in a normal seat as water is far better at applying forces onto an object than air as it doesn't compress very well. That said as the water applies the force onto the person, it will also apply the same forces onto all other objects around them as well. So it will appear "less turbulent" according to their eyes, but their insides will feel it far worse than had they been in a normal seat.
To do what your thinking, they would need to find a way to suspend the seat by way of elastic and springs, whilst that would help keep the pax relatively nice and steady, but it would cause absolute havoc for the planes ability to stay in the air, and would most likely exacerbate any turbulence for anyone not in the springy chair.
(Just thinking back to experiments I did in year 7 and year 9 science and year 11 physics, so do correct me if I did get it wrong)
