This Author's Life

Feeling somewhat frustrated, I'm almost at the 40k mark, and I feel like I can't add anymore to the story. My goal is really 50k. My friend told me that if I add a new character in it can add up to 10k to your ms. Now, my problem is trying to come up with a new character to my already almost complete ms. I want to make each relationship in the book complex and well thought out, so I'm not entirely sure I want to add in a superfluous character. Any ideas for what kind of new character to add in?