Thanks folks, I will check the seat map at T-72.
It's showing a 3-class 777 at the moment with rows 12-14 being WT+. There are 3 cots marked at the front of the cabin.
We'll probably pay for reserved seats anyway, particularly on the way back, as we don't want to be bothering with 'fastest finger first' seat selection in OLCI on the last night of our holiday.