I love
Sidony. I know a young girl called
Sidony, pronound sid-doh-nee. She's
Sid for short.
Sidonie I don't like quite as much. The spelling is too frilly and it's a lot girlier.
Sidney I feel is more of a girls name but could still work on a boy. However, I think it would have to be shortened to
Sid to make it more masculine.