First, check the limit of the bassinet of the airline you'll be flying. So far, Lufthansa has the biggest I know of. It held my big one year old. Most bassinets only fit babies up to about 6 months.
Emirates is 11 kg;
http://www.emirates.com/english/plan_book/essential_information/travelling_with_infants.aspx
Air N.Z. 11.8 kilos and 8 months
http://www.airnewzealand.com/travelling-with-children
Korean Air 11 kilos
http://www.koreanair.com/local/kr/gd/eng/cs/sn/eng_cs_sn_if.jsp
Lufthansa 14 kilos
http://www.lufthansa.com/fr/en/Children-on-board
Some airlines reserve bulkhead seats for those with lap babies and they go in order of the age of the lap baby, the youngest goes first. Other airlines have different policies. United, which you're not flying, holds bulkhead seats for their frequent flyers. Annoying to be stuck in seats with rows in front with small children and see all adults sitting at the bulkheads. Some of those links explain the airline's system for who gets them. I don't know of any airline that will guarantee it.
Make sure it's a wall mounted bassinet and not some box they sometimes hand out. For an international flight, it usually is but double check your flight(s).
Usually though, we bought seats for all members of our family and used car seats on board. I used to be a Flight Attendant and saw all the yukky pictures... Using a car seat also means that you don't have to remove the baby from the bassinet in turbulence, when they need to be picked up and held. Babies shouldn't be left in bassinets during turbulence and most airlines require that they be picked up.
If you fly with a lap baby, be sure the baby is not attached to you in any way. This is dangerous for take-off and landing because you weigh more than the baby so they're safer loose in your lap. Some airlines require the use of double seat belts (sometimes called "belly belts") to protect other passengers, even if it's dangerous for the baby. If that bothers you, book with a company that doesn't require this but the chance of a crash is very low so most parents go with the cheapest company.
If you buy a ticket for your baby, or are allowed to use an empty seat, double check that your car seat will be accepted on your airline. Some have odd rules, like requiring the baby to face forward (no infant bucket-style seats allowed). Check that your car seat is air travel approved. Email the company if you have further questions (do NOT call, they can say anything, write and print it up in case you get a different story at the airport).
Lufthansa is good about foreign car seats and has the bigger bassinet so although I don't have experience on the other companies (with babies), I can recommend them. I never get good deals on their sites and found booking through a travel agent aligned with them to find the best prices. But do everything; check the consolidation sites, the airlines' own sites and email a few travel agents so double check you're getting the best deal.