do you have a fairly good direction with your snowboarding, or are you still in limbo land where your trying anything and everything? are you comfterbly charging down the slopes and carving using both your edges strongly? flex may be another option to consider. im your size but just a tad lighter and ride a 158. ive heard my board is known for being a little stiff, but i ride with a pretty powerful and aggressive mentality (at least i like to think so. ha!). so i make it work for me.
if your wanting to hit a little of everything or still trying to pick it up id say maybe go 160-162. if your a natural on a board then you can make 159 work for you.
try sliding down the mountain on your toes with your back facing down the run. natural instinct usually makes it easier to do the reverse and stop on your heels. i found when learning that speed was actually a help assuming you know how to stop or at least slow down. its hard to get up on edge and learn to transition between the two without some inertia. usually we tell buddies to just skip the bunny hill. lol.
160 sounds like a good median... might want to research all mountain boards.