Just fitted swivel to my single passenger seat. Sourced from Kiravans. Straightforward job. Seat came off the base with four bolts. No wires to detach (mine is a basic model, no electrics and no seat height adjustment).
Jack has to come out and another home found for it. The four mounting bolts for the swivel base fitted perfectly. I had to the following work to allow the finished seat to swivel:
Remove the two torx bolts from the front of the seat base (they don't seem to do anything).
Remove about 10mm from the protruding pips beside them (and fettle and paint the amputations).
Remove the top brackets for the rear seat base plastic trim (seems to remain in place without them).
Remove the lower lips on the plastic seat trims (just the bits that fold inwards, so very little and really not noticeable).
The drop-down fabric trim at rear of seat will need to be shortened.
The passenger door has to be opened when swivelling in order to avoid the rear of seat rails scratching door card, which I don't mind doing.
Seat sits about an inch higher than before. And it's a sound and sturdy arrangement, no rattles.
The whole job was easier than I anticipated.