I'm not one who worries about popularity so I say go for it. Plus Sophie is a lovely name and will work throughout her life. I go for names where I can envision a baby, teenager, middle aged and pensioner being able to pull it off, and Sophie definitely works under my criteria
I'm not going to worry about how rare/common names are. If you like it, use it.
My name is common and I was one of 4 in my half of the year at high school. It never bothered me and nobody ever really brought it up. As an adult I haven't personally met/known someone with my name in years!