Not sure you will be able to get the seats much lower to the floor. The way most replacement seats work, is you keep the unique mounting for your car which is designed to bolt correctly to the floor, and sit level, taking into account any lumps and bumps in the floor pan, and then the frame on the replacement seat bolts to that mounting, the reason the T2's mounting is so high, is it has the up and down adjustment built in.
Fitting another seat is easy enough, there are a few threads on here where people have fitted other car seats, but I think most will have used the original mounting frame, so that would not really help you...
Just as a matter of interest, how tall are you, as I am 6'1", and the car has tones of head room for taller than me.