Just wanted to chime in and let other FF moms know that a formula-fed baby won't necessarily get sick either! When I went back to work, DH took two weeks off to take care of DD. Unfortunately, he came down with a really nasty cold right before his time off with her, and it lasted for the entire two weeks that he was her primary caregiver.
I had stopped BF several weeks before, so DD was being entirely formula fed (she was never EBF due to low supply), and she never got sick. DH just made sure to wash his hands very frequently and limit his contact with her face. He also slept in the guest room (LO is in our room), because he was coughing really badly at night.
Anyway, just wanted to put that out there, since I know I felt (and still feel) really guilty about not breastfeeding, and seeing stuff like this would always make me feel worse.
To the OP: good luck! It sounds like you're doing everything you can, so hopefully your LO won't get sick!