Depends on how you want to surf mate, I'm 5ft 9" and 12 stone with a 6ft 8" board about 2 inches thick, which is quite small as it goes. Generally the shorter the board the larger the wave needs to be to get up on however once your up your more agille and quicker. The larger the board the more buoyant it is so its easier to get up on smaller waves (longboards etc riding pretty much nothing) Best bet would be to goto a surf shop and get them to measure you up for a board so you know what length and thickness would suit you, then go away and get something second hand off ebay

Alex