In one of my rooms I have a sofa which is close about 8 years old which is still really comfortable. The problem is that despite washing the cushion covers, it's starting to smell like it has had 8 years' worth of use. Any ideas for making it smell neutral or clean?

Most searches I've done recommend putting the cushions outside for a day, but it's fall and it's cold and cloudy so I'm not sure how that'll work. Plus birds may poop on them. I vacuum the couch and use fabreeze every week, but that's only masking the smells for a short time.

I'm thinking sprinkling baking soda on the inside of the cushions... not sure if that'll work. Any ideas?