What size snowboard should I get? (read the detail)?

I am 11 years old and i am getting a snowboard. I have only snowboarded once on a school trip, but I discovered I am extremely good at it. i can do tricks and everything, i can go down the black diamond without any falling or anything. I have a shoe size 6 and 1/2, but i can also wear a 7. I am almost 5 feet tall, like 4 feet and 11 3/4 inches. I weigh like 84 pounds, and i don't know what size snowboard to get. By size snowboard, I mean like 130, 145, 180, etc. please help ;)