I would prefer two types of marriages, civil and religious. You can have one or the other or both.
A civil marriage would be between 2 consenting, capable adults. It would grant them legal rights, obligations, responsibilities, etc.
A religious marriage would be celebrated within the beliefs of that religion. It would not grant any legal rights, obligations, etc. This type of marriage could be used by persons who want to maintain their legal individual status. For example, this could be used by persons who would otherwise lose their disabillity support if they had a civil marriage.