Shortboarding

I'm 5'3'' and 115 and have been surfing for a while, I'm very comfortable on a longboard and a fun board, but i really want to get into short boarding. I have gotten up on a 5'10 and a 6'4 in hawaii with a surf coach but it wasn't easy. I have a Lost uber plank but i don't really consider that a true shortboard since its so wide and floaty. How big should i go with a shortboard for moving down? should i get like a 6'6'' so its easy to paddle and floats me? The waves where i live are usually small beach breaks from 1-5 feet