I feel your fear! I traveled with my daughter alone, 21 hour flight in all, when she was 7 mo. She did not sleep at all, (I didn't try any of those methods, also worried about side effects—and melatonin never helped ME) and tho she was ok on the plane, she screamed like she was being murdered the whole ride home. Then once in bed she promptly and gratefully fell asleep. So at least, don't fear ramifications once you get to your destination!
I will say this, though: however you feed him, bottle, breastmilk, try to arrange a feeding for takeoff and landing. The swallowing helps prevent the ear pain from the change in pressure and trust one who knows from bitter experience, that's a screaming baby you'd like to avoid!
DEFINITELY get the bassinet seat if you can. The bulkhead seats, where they put the bassinet, have more legroom anyway!
As to lavender, I don't know if it works, but it sure smells good. Mix some straight lavender oil with olive oil (20 drops into 1/4 cup or so) and rub it on the bottoms of his feet. My daughter loves that. It is also a really effective preventive/cure for diaper rash.
Good luck!