Lightweight fleece blanket. Doesn't take up much room, whether spread out on a bed or folded neatly and draped over couch. I have the green, twin XL, which I use as a couch cover to help control dirt, fur, and damage from 2 adults, 2 large labs, and 4 cats. My couches are old, but I still like to keep it somewhat clean. I tuck the blanket into the cushions, and since it is a fleece material, it stays nice and snug. I love using fleece blankets for this purpose. Fleece has some stretch, so it works well with tucking it tightly into place. I much prefer fleece over sheets, other blankets, or even those covers that are meant for protecting the couch. I don't bother with covering the back of the couch, but if I did, I would either by a larger fleece blanket, or use another twin and tuck that into place. I included pics so you can see how I do it, and what it looks like overall.
I also use it as lightweight blanket for when I am lounging on the couch. I like that it neatly folds together, and doesn't take up too much room, yet I feel comfortable with it when I am feeling cold. My cats like curling up on it, too.
Easily goes into the washer- I wash two at a time. (I bought four- one for each couch to use as cover, 2 for swapping out or for use as couch blanket).