Correct me if I am wrong. that is a polini pocket bike seat, and should be about the size of a pocket bike seat. From memory, I would say that the seat is about 7-8 inches wide at its widest seating area. over all I think its about 18 inches long. its comofortable enough for me, but i road a moped around for a month sitting on the rack.
If you have an adhesive pad you could stick it on literally anything, even a pocket bike seat. I believe that they sell pocket bike seat padding foam.
Installation on my bike would take 5 min, drill some holes drops some bolts. Its gonna be different on every bike.
Try this, Stop being a pussy and buy one, they look rad when done right, and if you can't figure it out and havent fucked it up I will it from you, at a small discount of course