but the example he gave is vocative (wołacz) so that should be moja miłości except does anyone use vocative for that?
This phrase is just perfect as a phrase in vocative, with the exception that it should be put in the reverse order:
miłości moja! I am not entirely sure what the OP wants to express, but 'moja miłość' which is also good is just a descriptive phrase, whereas 'miłości moja!' says the same, but directly addresses a person who is someone's love. The latter phrase is vocational, affectionate and very poetic. In plural it would be:
miłości moje!