Warm but cool!
You can read more @ my blog, there are more photos too, they'd be helpful.
Lay your boule over a paper sheet and trace its silhouette with a pencil.
Add a couple of cm all around the outline and cut your template.
Lay the template over the felt and cut out 4 pieces.
Set 2 pieces aside (they'll form the front of the cover).
Take the other two and cut them in half lenghtways (they'll form the back).
I worked on the back pieces, adding some ribbon as decoration and then sewing the buttons on the left side and making a loop on the right one with some elastic cord.
Then I sew them together.
Now you can asseble back and front pieces, sewing them together with blanket stitch.