* Guten Morgen, meine Liebe: This is a very common and sweet option. "Meine Liebe" translates directly to "my love," but it's often used affectionately even with someone you're not romantically involved with (like a close friend or family member).
* Guten Morgen, mein Schatz: This is even more affectionate, translating to "Good morning, my treasure." It's best reserved for someone you're very close to.
* Guten Morgen, meine Liebe/Mein Liebling: "Liebling" means "darling" or "favorite" and is very affectionate.
The best choice depends on your relationship with the person. If you're unsure, Guten Morgen, meine Liebe is a safe and generally well-received option.