Couple of questions iggy.......

Was it a traditional surfboard that u demoed or specific kite surfboard?
If traditional do u plan to ride it in the surf without the kite as well?

Rule of thumb for traditional surfboard is for the board to be 2 inches taller than what u are and I would think with a kite surfboard u could afford to go a little bit shorter as most seem to have a bit more volume than traditional. So keep demoing and I would try some of the larger ones considering ur weight and height.
Most of my mates and myself bought a cheap old dinged up sb to start with and practice on........just a suggestion

Ohh, and keep persisting with the strapless riding and practicing ur gybes, it'll be well worth it when u get it dialled

.....I would also recommend getting urself a copy of the Ben Wilson dvd Smack

Good Luck!