Chelsea and [name_f]Chastity[/name_f] were the first two that popped into my head, although I know you said you weren’t fond of [name_u]Chelsea[/name_u] (neither am I and it’s my name. lol). I honestly think you could get away with [name_f]Chessie[/name_f] as a nickname for most names beginning with Ch-. Like [name_f]Libby[/name_f] is sometimes used for [name_f]Elizabeth[/name_f] or [name_f]Peggy[/name_f] for [name_f]Margaret[/name_f]. You don’t have to have all the sounds in both the original name and nickname. You could also do a Ch- first name with an S- middle name and get the nickname from there, as well. Also, random rabbit-holeish note–a meaning for [name_u]Chelsea[/name_u] is often “chalk or limestone port/sea port” so [name_f]Chessie[/name_f] with that meaning is likely a variation of [name_u]Chelsea[/name_u].