I'd have to agree with brooklyn that the maize/slip bag does work wonders.
This kid kinda knows what he's doing, this would be a good way to start out on the maize ball.
YouTube - Slip Bag / Maize Bag Boxing Training In Pittsburgh
Also, if you've kickboxed for a while, you should already have a good foundation in boxing. Its different but at the same time its not all that different. Im suprised that you don't already have some training in boxing because thats a pretty big component in kickboxing, you must have got hit ALOT.