It is a lot of preference. There are some people that are 140lbs that ride 140 and greater boards and then there are 200lb people that ride smaller than 140 boards.
You will hear different arguments both ways as to why smaller or larger is better. However, in general, the heavier you are, the large the board you will want. I think the 140 is just fine for you. I am 200 and will ride 140-142... I would even consider the 147 era for a test ride.