I have a small living room and couch is sitting against back wall... Hence ceiling speakers would be best.
So the question Is, worth doing a 7.1 ?
since the seating is against the back wall, it probably won't do much for you.
and may even sound crappy.
my advice : get 2 extra speakers. make temp stands for them = yes, large enough to hang them above you. some 2x4's and screws will do the trick.
then experiment with placement.
if you like the results, put the in ceilings where you like them. if you don't like it, you didn't spend a lot of time, effort & money, for nothing.