L.Z.
Get a wrap...Wear him for his nap. I would look at Moby wraps/ Ellaroo. I have both. Ellaroo is a bit more versatile and not as long and warm as Moby. This would also enable you to allow baby to sleep on the plane very easily.
Look into other babywearing possibilities besides a Baby Bjorn, which carry the infant by the crotch. YOu likely have a babywearing group that meets near you.
http://www.mamatoto.org/Default.aspx?tabid=36
We traveled with 4.5 month old and borrowed some items because we could from family that we were visiting. However, pp suggested renting items....I looked at that and you might as well buy the item because it is quite pricey.
Best wishes