When you say putting blankets on them to cover them during the day doesn't work, do you mean that they don't stay in place? I think you need slip covers because they are made to fit the individual cushions as well as the frame. How often do you have company? It might be a paint to take them off every night but if it's only occasionally, slipcovers in a very durable washable fabric could do the trick. I know you can also purchase furniture throws for this purpose. The backing layer is a soft foam which keeps the fabric from slipping around too much. I hope your furniture isn't leather because leather is so slippery there's really nothing that won't slip on it.

We used old queen sized quilts to cover our "nicer" piece. They were large enough to hang over the back and thus not slide off the seat portions.

Try a painter's canvas drop cloth. Buy one that is large enough to drop over the back almost to the floor and go almost to the floor in front: 9x12 or 12x15 feet.