I've never bought shoes online, because of this very problem, but I need slippers. I bought size 9 and they are too tight to get into and their sole is exactly 1 inch shorter than the slippers I have now that fit.
If 9 is too small, what size would be one inch longer?
Googling has just confused me. It says that one size bigger is 1 barleycorn longer, 1/3 inch. That would mean I need a 12 and I'm sure I never bought slippers in size 12, plus it would mean people with feet an inch longer than mine would need a 15!!!
I wear an 8 1/2 shoe so I thought 9 was good.