Lots of people have them, even my contractor does! You need to pull a new GFCI circuit for it as PP said.
We installed one last summer, an entry level model.
https://www.amazon.com/dp/B0999L5S2F
So you can put the Washlet on top of an existing toilet IF the neck of the toilet (where it meets the tank) is a straight wide one, not a tapered neck. We had a tapered Kohler and it wouldn't fit, so we ended up having to order the Toto toilet as well.
Also you can decide if you want the Washlet+ which means the wires are hidden. But if you do you must buy the Toto toilet b/c it has an extra large hole in the neck to fit the bidet with the hidden wires.