My first Swiffer Mop cover was a bit narrow (see Mop Cover #1 here). So I attempted to make it wider; Mop Cover #2 looked pretty good (see Mop Cover #2 with modification details here). It fit better than Mop Cover #1. Well here's a photo of Mop Cover #2 after washing:
It shrunk a wee bit, but it still covers the surface of my Swiffer mop. :-)
And my mop looks good from the top too...