Can i travel with 3 month old baby for 9 hour flight ...?

hi pple just wondering if i can take my 3 month old baby on 9 hour flight would that effect his health even thought she's healthy and i have her on lap seat because its really expensive now the airfare (polish lot)... is about 2000 and its an emergency situation that i must travel now and is it ok to put him on a car seat in the airplane even though i have her as a lap seat... pple im not stingy lap seat cost ( 599 $$$ ) any way so any suggestion please fast answers plzzzzz.... THX...