I have an expensive couch. All of a sudden it feels like I'm going to slide off of the end.?

No matter what I do like fluff the pillows or re-arrange them it still has the look and feeling of going down a slide. I have seen the infomercials about those slidder things that go underneath the cushions but I don't have the money to order them right now. Does anyone have any ideas on what to put underneath the cushions to give it some stability? Would be getting a piece of lumber cut to the exact measurements and putting it under the cushions temporarily help? The couch is not but a few years old and in perfect condition. I need a temporary fix. Any ideas?