Jan - the most important thing is to always remember the airline safety instructions. Your baby depends on you. On your mood, your functioning, and your health and wellness. Your baby does not need sacrifices from you - your baby needs a reasonably happy and moderately active mama. Right now, from the way you write, you seem to be in the self-sacrificial mode. This might wear you down and cause a burn-out, which won't do the baby any good. Put your oxygen mask on, whatever it takes. If it takes formula, so be it, but the baby is most likely old enough to reject formula.

I see a lot of moms and dads with baby joggers around. They seem happy and the babies are sleeping soundly in the joggers. I have never had one myself, but I observe people around me and see satisfaction on their faces. You are on the East Coast, so this is probably not relevant right now, but come spring and you might want to invest in a baby jogger. I am sure you can buy a used one.