Duvet Cover

My mom had asked me if I could make a duvet cover for the twin duvet we have. I've never done one before but assume it has to be pretty easy. I had a quilt top that I finished last year and never quilted so I decided to add onto it (to get the right measurements) and then use it as the duvet top. However, with all little pieces (I read online) that it's best to sew/quilt the top to a solid piece of fabric (ie. an old sheet) to give it some stability before attaching a back to it. So after expanding my original pattern, I pinned the back- now I just have to find the time to finish this project!