I found these slippers to be small on me, therefore, they were uncomfortable.
I normally wear a 7.5M or an 8M. Most reviewers stated these slippers run large, so I ordered the 6.5 - 7.5 (M). When I put them on, the length of the shoes was more than long enough, but the band that goes over the top of my foot was way too tight.  It was painful to walk and I didn't know if the material would stretch or not, so I returned them.  My foot is not especially wide, so I am not sure why these didn't work for me. I definitely think the next size up would have been too long (in the length).