The following video by Laura of Sew Very Easy demonstrates how to measure your sewing machine and stitch together a cover that fits just right. Her instructions are very clear and easy to follow.
Use two or three fabulous fabrics, as she does in the video, or decorate your cover with quilt blocks, patchwork, embroidery or fancy quilting. The “look” of your machine cover is totally up to you. You can also add pockets for stowing this and that.
Batting will give your cover some heft but Laura prefers to use a product called Support, made by Fairfield. This is a thin foam with lightweight fabric on each side. It can be sewn into the machine cover just like batting and will allow the cover to stand up on its own without sagging. It gives a nice finished look to the cover.
A similar product that works just as well is Bosal In-R-Form Foam Stabilizer. You can purchase it here.