I always get thin Vibram soles put on them and they never look thicker or bulkier. It makes all the difference to the grip when I walk and to prolonging the shoes' lives. I swap them out at the cobbler when they get a bit too dirty, but the threads are always still visible. I've only gone to that one cobbler because good quality Vibram soles, plus they'll polish to blend the new sole to the shoes so they are never obvious!
I usually wear them out once or twice weekly on the weekends, and do extensive walking because I rely on public transport to get to places. Anyway, I wear socks as long as I have covered shoes on to prolong their lives (even Converse; it feels too gross to go without socks), and so I have tiny ones for my Repetto. The insides of both my Repetto are still white and smell-free due to my sock-wearing habit, though the sides are darkened due to exposure to accidental rain puddles over the years. I've actually decided that if I were to be caught in a thunderstorm (frequent) in my shoes, I'd either stay indoors or walk barefoot
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My feet are quite large and wide, and some of their shoes are cut on the smaller side without as much give; basically depends on the leather. I hate thick shoes because they make my large feet look bulky, so the thin soles on the Repetto are perfect for me. The only bad thing is I can never get the bow to lie nice, so they are *always* wonky. I see that as a casual awesome thing though.
Despite the high price tag, I love how they look and will always want a good pair with me. I have been recommended the cheaper French Sole by my friend, but I'm not sure I want to explore another ballerina flats brand now.