If I sit on the floor, will my body be under more pressure than when I was standing??
Yes, very slightly but you won't feel it that way due to you spreading out your mass on the floor.
it is similar I suppose to sitting in 6'of water, in the denser medium you can really feel the pressure difference at the bottom.
Yep; water is a good analogy for what's happening. the reason people can't equate it to air pressure is the very fact that we live under air pressure and are basically "body wise" equalised to it because we are just a collection of molecules or water and atmosphere condensed together.
Having said that. If we try to use the depth of water as dense pressure upon us, the arguments come out to say that we float and it's hard to get it into people's heads to disregard the floating human.
This is why some come out with, " well surely we would float in air with your denpressure, scepti."
People can't seem to get their heads around a stacked atmosphere, just like stacking a swimming pool with water. The highest pressure is obviously going to be at the bottom and the lowest pressure being at the top.
So "IF" we use this as that analogy, we can then imagine picking up , say - a 4x4 feet sheet of metal (for instance) from flat on the deck. Now you can imagine the force upon that sheet of metal as you tried to pick it up against the mass (pressure) of water bearing down on it.
Now imagine trying to throw that sheet, upwards?
Obviously to understand it being the same, we also have to imagine a person being acclimatised to that environment as well, which naturally means they are denser than the water and can walk the bottom, just like we do on land.