I think you are right in that getting her a perch to have near where the couches are that she can use. She probably likes being near where you are (hence the back of the couch), so having someplace for her in the same room, with a similar view of the surroundings would probably help. We have a little round tower for my cat at the end of the couch after the side table and he likes it there.
There are products you can buy to spray on the furniture to keep them off (the scent is unpleasant to them but supposedly neutral to people... I don't know, I haven't used them).
I would do them in sequence... buy the perch, tower, whatever and then when she starts using the perch immediately implement a method of trying to keep her off the couch - a spray, foil, the tape and keep at it for a few days. There is even a spray you can use to attract the cat to the perch if she doesn't take to it right away. Some suggest using catnip on the perch, but I find that is more stimulating than calming. I can't remember the name of the "atrractant" spray, but maybe someone at PetSmart or PetCo would know what it is.
Good Luck!