Hmm, you are pretty light and you mention you learn easily/flat water it is easier to handle a smaller board as it is not as choppy as open ocean (even if you typically use a smaller board on the ocean, bigger on flat water/fresh water lakes due to buoyancy and better planing). But with above plus your sail range, I tend to think you might actually be able to get a Gecko 122 x 77cm width. Definitely fits the sails better and your weight, so it would be a good board to advance with too, even if a touch small at first?