What I have done is bought cheap surfboards off craigslist to see if the size fits me. I would say for your weight a 5'8-6'0 thruster around 18"wide and not too thick. So the best thing about doing it this way is if you dont like the board resell on craigs list or maybe one of your kite buddies could try it out too. Surfboards are so dang expensive and thier are soo many sizes and shapes. I just got a 5'11 with 2 sets of fins for $45 off craigslist.
If I dont like it of put a foot through it no biggie.