Second or Shortstop would be good for you. Usually first and third basemern need to be tall, as they would have a better chance at catching high lineouts or filelding high or off the mark throws (especially firstbase men.) As I mentioned in the Houston thread, Jose Altuve is an excellent second baseman. He's a great fielder, and he is only 5 '5.
I guess for catchers the size is not relevant? And outfield? Isn't it more about being at the right spot at the right time?