hi oliday
We never actually assembled the sofa bed, but it looked like a small double. I am sure it will be fine for one child. If you do spend time in the room and need a bit of extra space, perhaps you could fold it up during the day.
I really wouldn't worry too much as you say you are not in the room much anyway.
Don't know about the main part of the hotel but accross the road were we were the 2nd floor rooms have a kind of vaulted ceiling which is quite high and gives the room a spacious feel, so they do not seem claustrophobic at all, infact they seem quite light and airy.
We had two first floor rooms, next to each other at the end of a run of rooms and my hubbie commented that it was like having the upper floor of a private villa to ourselves
This is a good hotel for Turkey, you have nothing to worry about.
Doe