I haven't said anything to my SO yet. I want to be sure I'm ready to actually follow through with it before I say anything.
Sounds like you are working out a plan with mom. WTG!
Great that you are focussing on what you DO want -- to be ready to actually follow through.
Almost ANY infant "bucket style" carrier is good. That hard kind with the handle? Your kid is that small right? Bet you have one already. Look at brand, look up manufacturer number, call up their customer service and ask "Is this carseat model ____ approved for airline use?" if you need the reassure.
I feel like telling him is going to be the hardest part.
So just don't tell him right now if it hurts your "follow throughness." Sounds like you know yourself pretty well.
You can choose WHEN to tell him. You can always tell him after. The convo would still be just as hard for you, right? But the main part will be over with.
Could even choose not to tell at all! YOU can choose the choices in YOUR life.
Start learning to think about what is less stressful for YOU. (You can learn that from his example!)
Hang in there. I keep hoping you get yourself to a happier place and a brighter future. However it is you gotta go to GET there. Will be rootin' for ya and baby.