Staying true to my Yorkshire mining family roots and saying settee and living room, although I have moved on from having three legs and a house brick under the settee, as my poor old Mam tolerated for years.
Used to say settee but recently bought two sofas from 'Sofology'. They'll be in the front room. When my DD set up home she still called her sitting room/ lounge the front room even though it was at the back of the house.
I've never used couch myself, but don't have anything against its use. I had imagined that it came from the French verb coucher', but a quick check on WordReference shows that the Fench noun ^couche is sometimes used to mean 'bed'.
To me, either of those roots seems likely, and as my OH spends half his time lying on this piece of furniture, I think we should start calling ours the couch from now on!
Sofa. Couch seems to be what the Australians have in their "lounge room!" I was taught that lounges were only to be found in an hotel or at an airport.
I haven't heard the word couch used in UK for anything other than doctors' couch, but it is quite widely used in USA. 'Lounge' reminds me of hotels and airports.