The Isotoner ballerina slipper is very comfortable.  I use it for Tai Chi practice.  I ordered the medium and discovered it was too small.  (I usually wear size 7, and the medium is supposed to fit 6-7.5.)  I passed those slippers on to a friend who is a size 6.  They fit her fine.  I then ordered a large for myself, and am very happy with the slippers.