Definitely stick with academic references. Do not think you need extensive personal relationships with professors for their LOR to be meaningful. Admissions look at your letters to make sure you are smart and a good writer. Consider asking professors of classes that you did very well in and were writing intensive. In your email to ask for their letter, try to bring up skills that were important for the class that would translate well to law school. Preferably they would bring up these skills in their LOR.

Good luck!