Welcome to FT..! Well, your second post anyway...

There are 2 types of baby cots / seats available on board - cots for babies and sky seats for infants as described in the earlier post which will probably be better for the 7 month old. They can't be prebooked but there are a number on board long haul flights and when I was travelling with babies and infants there was always the right type of seat available for us. Just ask when you board.

Stick with 20EF - by far the best choice in your situation!