(Assuming you're a US citizen:) There's no cosigner needed on Stafford or Grad PLUS, and those together will meet your cost of attendance.
PLUS requires a "credit check" but I believe you only get rejected if you recently went bankrupt or some similar black mark, NOT just a lack of credit history (because, after all, it's a loan to a student, and in many cases, we're pretty young. And law students are NOT considered dependents, so your parents' background is irrelevant here.).
The federal government created these loan programs to ensure that everyone can get an education regardless of where they came from. Being from a low income background shouldn't hurt you.