I knew a REALLY DUMB GIRL named Cozette. Like, REALLY dumb. I do think her friends called her Cozy, but I bet they were also dumb.
I used to think it was kind of cute before her, but now I think it's comically ditzy. The problem with
Cosette is that, aside from sounding cute, it's really got nothing behind it. It was even a nickname in
Les Mis, and the comments don't make it sound like it was a particularly strong nickname. It sounds like "little thing" to me, as Cosa in Spanish is "thing" and -ette is a diminutive. I wouldn't want to be named it. But I think it would be kind of sweet as a middle name, and since it's an iamb it could go easily with a lot of stuff.