Personally I would suggest a foam board over the epoxy or carbon fibre boards. Something nice and thick, with xlnt bouyancy to support your weight. I would also suggets something fairly wide, this will allow you to balance yourself more easilly while you are learning to knee paddle.
You'll have lots of fun paddling out past the breakers, standing up just as the wave approaches you and getting the view of your life of the oncoming sets. Nothing easier than knee paddling during your take off either, you can get your board moving much faster by knee paddling on the take off. Good luck!