Hi - we are booked to fly LHR to BKK on EVA, economy class, in February. Our daughter will be just over 10 months when we fly back 2 weeks later. We have 3 economy seats booked and an infant in arms ticket for the little one. I asked lastminute (through whom we booked) if we could pay and upgrade the infant ticket to a seat but they said not. A few questions:

1) Does anyone know whether EVA would upgrade our infant ticket directly:?
If not,
2) should we go for the bassinet or not? I think the arms on our 3 seats will not raise if we go for the bassinet. Alternative is to go for 3 standard seats but raise arms and hold her/sit her next to her sister once we have taken off.

She is about average weight and height now at 6 months - currently about 16lb. We fly out on night flights and she is the kind of baby who just sleeps from 6pm to 7am - so likely she will sleep for the bulk of the night flight which leaves 10ish i think from memory. Coming back we leave at 1pm - so she would probably sleep half of the flight. She is also the kind of baby who hates sleeping when held...likes her cot.

EVA book bassinets from 100 days in advance, so from next week so trying to decide now!

If we book, will we be able to revert to normal seats at the airport if she is to big or if economy is not so busy and we could get a spare fourth seat next to us?
Any advice gratefully received!
Looster