This is my third pair of Old Friend Juliette slippers.  I am so disappointed in this pair.  It is clear that Old Friend cut back on the material that goes into each product.  It affects fit, size and comfort.  In my original pair I have a good 1/2" more material all of the way around.  It is a true size 11.  This new pair, is much more narrow.
I'm going to keep them.  I really hope that over time they will stretch.
You may want to order a size up.