I think it depends on what part of the country where one was brought up re what it is/was called. In my part of Scotland it was called a settee but in London, it appears to be a sofa.
Maybe it's a northern thing charleygirl I'm from Yorkshire and call it a settee. We bought some new rather expensive settees Merlotgran and had to retrain the dogs to keep off them. It's successful about 90% of the time my husband has weak moments !!
Are we doing U and non U here? I call it a sofa and have done for years, but as a child ( growing up in the North) it was called a settee. It’s in the living room or lounge depending on how I feel at the time. Never a sitting room ( although we do sit a lot) and certainly not a drawing room.
My Sofa is in the lounge, it can't be the front room because that's the dining room and the lounge is at the back overlooking the garden. I'm a Londoner born and bred and as a child we had a settee, it became a Sofa when I got my own place and has remained a sofa.
I've given up trying to keep the JRs off the sofa/settee. I bought a sofa throw but they like to scrabble it up to customise their bed so I bought a throw to go on the throw.
I have 2 settees in the living room. DS is now wondering about the new kitchen/dining/sitting extension. Should the 2 new settees be in the sitting room (at front of house) and the slightly older leather ones at the garden end of the extension ( where there are doors out to the garden) and what should the different rooms be called? There won't be a separate dining room but table and chairs will sit between kitchen and sitting areas. Someone must have this arrangement so is the whole area the kitchen? Or is it the living room? Can't go on calling it the extension and garden room is a bit pretentious.