W.L.
I have never traveled with my son, but I too have a 16 month old and can only suggest that you buy another seat for him. Not only for the safety fact in case of an emergency, but who wants an antsy toddler sitting on their lap for anything more than 10 minutes! If he gets scared, you can hold him, but at least you have the extra seat as back up.
Good luck and you have really received some good feedback from the other moms who have some good ideas.