I was thinking the same thing while mowing over roots a couple of days ago. A air ride seat would make it a lot more smoother. I don't know of any for the BX but if there was I would diffenently look into it.
LOL. I keep thinking of Oliver Douglas in the opening sequence of "Green Acres". He tractors by, bouncing 12". Might be more fun with Eva Gabor in your lap...
Would think an air seat might make keeping the hydro pedal steady a little difficult. Guess you could keep your heel on the deck. Never seen an air seat that would fit a BX though.
The air bags used for air ride seats are very large in size and you would have trouble with reaching the pedals and the seats are very very expensive and would require the use of an onboard compressor and may make the riude much worse because of the short wheel base of the tractor-essentailly turning it into a trampolene.
Perhaps you shold look into having the rear tires loaded as that also works very well to soften the ride-the air in the rear tires is simply acting as a balloon and reacting to the speed of travel during work.