1991 Pontiac Lemans Door Lock

My passenger front door is broken. The door latch that holds to the side knob has broken and I don't know whether i can get it fixed or if I should buy a whole new door. The door wont stay shut on its own so I had someone pull the panel off and tighten the latch so it holds onto the side knob that sticks out. So now it just stays closed. I'm just tired of everyone having to ride in the back seat. What should I do?