I'm just under 90kg and the float of the IS111 is fine for me. In fact today I used a 9m sail on it all day, ranging from 8 knots to 20.
The Supersport is a great board, but if you're used to slalom boards it may feel a bit soft, particularly compared to your CA. I even found that my IS111 felt soft after the Fanatic falcon 111 it replaced, but I'm used to it now.
You may want to try a demo first.