Switching from breast milk to formula

Okay, so after this week I will be out of breast milk. For the first 3 months she had strictly breast milk that I exclusively pumped.. at her 3 month appointment her dr told me to start adding rice cereal due to her severe reflux and laryngomalacia. (She is on medication for that also.) For about a month and a half I have been supplementing at night with Similac for Supplementation. I am not sure if I should switch her formula, or leave it as is since she won't be receiving anymore breast milk. Thoughts?