We did a similar return flight OSL-DXB, and I would advise you to get the bassinet seat. If not for the infant, you can use this room for storage / toys / etc, instead of using the leg room (believe me, there will alot of bags, and little leg room). Our son didnīt sleep in the bassinet, by we could place him there and he would play a little (he was around 6months at the time).

The bassinet seats are also close to the bathrooms, which are REALLY handy if someting should happen.

Pro tip: if the infant canīt sleep (because of noise/light), take her for a stroll to the back of the plane, and go into one of the bathrooms there. Close the door, but do not lock the door, as this would make the light turn on. This is how I (finally) got our worn-out son to sleep. And bring a blanket to put over her head when you go back to your seat.