Supplementing?? Help!

Elizabeth • 28 year old, happily married! Two miscarriages within 8 months. Praying for our Rainbow baby*
My little guy (16 days old) is up to about 3 oz every 2-3 hours... I've been pumping exclusively and my small stash I had in the fridge is quickly dwindling down. I only have about 7 oz back up right now. I'm doing every thing I can to bring up my milk supply. In the meantime I feel I need to be ready to supplement with formula.... This is very difficult on me as I never "planned" having to do this, but I know it's best for the baby right now. 
There's sooo many to choose from! I go back to the doctor this week so I will confirm with them but, what formula do you supplement with? I have samples of Similac for supplementation that I am leaning towards trying. Any suggestions? Words of advice? I'm so nervous about this...   Thank you in advance! ❤️FTM