I reupholstered a couch and chair with sheets on sale. I bought king sheets so I would have few seams and just draped them over the furniture, used my blue wash out pencil to mark sew lines, gave it a 5/8" seam and sewed. I put plain skirts on them with pleats on the corners and center of loveseat and 3 pleats across front of couch. I put zippers on each corner of the back. I gave it about 8" ease under the backrest and where the cushions sat. They came out perfect to the great amazement of my in-laws who were wintering here at the time.

Life was sweet and I did it cause no one told me I couldn't.
Actually, I probably would have done it even if they said I couldn't. I have a problem with limitations.

I have slip covered a sofa in white and in denim both turned out great.