Oatmeal cereal

Hi, my infant will be 2 months on June 12th. She has been spitting up after her feedings. She eats 120cc every 3 to 4 hours. I burp her after each feeding but she continues to spit up. She is on enfamil ar. Pediatrician recommended if she continues to spit up introduce rice cereal to her bottle so I am thinking about beginning her on Oatmeal cereal instead of rice. My question is what type/size of nipples should I put on her bottles?? I only use dr browns bottles and she's currently using level 1 nipples. Thanks in advance.