took my 6 month old from ATL to Belgium.a 8/9 hour flight.we did not buy her a seat. but did call the airline and asked for a bassenett seat. you will have to hold her for take off and landing and them they have a bassenett attachment that attaches to he wall in front of you. (you must sit in the bulkhead seat). no extra charge and still plenty of room for my husband and i.Not all airlines offer this so you must check and see if your flight and ailine offers it. we fly delta and i know they do on alot of there flight.
good luck and have fun! we will be there in May. ADULT trip this time...

We have never not purchased a seat for our children! If there ever was an emergency I always knew my children were securely fastened in their car seats and they were much more comfortable when sleeping!! Plus then my husband and I were free to have our space! Not buying them their owns seats and bringing the car seats has never even been an option for us! I would buy her the seat-bring the car seat- and watch her sleep peacefully and safely while you and your husband have your own space!! as for her crying if I paid that much more money for first class the last thing I want to hear is a baby crying!! My husband flies 1st class for business every month and has never seen a baby in first class. JMO though

good advice, i'm glad i read it...