We are doing the same. The room can also be a guest room if it has the ability to be closed off. We also added cavity doors to other areas of the house for heating and cooling efficiency. An open plan is nice but not always practical.
My thoughts exactly on closing it off !
Sorry for the novice question, but what exactly do you mean by a 'cavity' slider. Does that mean the slider door recesses inside of the wall ? as in between 2 courses of brick
Yes, cavity door slides in between the wall. Internal walls are usually just plaster.