Hey Bex, from my experience flying with DD when she was little:
You can't wear her in the ergo during take off and landing - they have to be strapped in with the infant seat belt for take off and landing. I asked why (I had DD in a Moby) and they say if something happens to me then they need to be able to get DD off me easily. Made sense. If the plane crashes and I'm floating face down in the ocean then a baby in a wrap on my belly isn't going to do very well!!!
It will go so fast! I was so nervous that DD would cry and get bored and annoy everyone! Between the anticipation of take off, and the anticipation of landing, you get probably 20, maybe 30 minutes max of just sitting in a flying plane. That said, we were once delayed for an hour when DD was a bit older, and we all had to stay in our seats on the plane. DD was not amused by the end of that - no movement, no noise.
And yeah, if bubba is sleeping, you can just sneakily make it look like the infant seat belt is securing bubba
If your DD will take a pacifier then bring one to pop in her mouth for take off and landing! Save her poor wee ears from popping!