The easest way to find your story's thematic statement is by considering what you want to do with your story. Think beyond writing a good story. What are you actually setting out to say or do with your story to make it good?
Multiple thematic statements will cause a lot of confusion both for you as a writer and for readers trying to understand the story they are experiencing. Stick to one powerful thematic statement, deepened and developed by connected themes that show your thematic statement at different levels and aspects.