Formal:
* Tout mon être: This is the most literal translation, meaning "all my being". It is a very strong and passionate phrase.
* Mon univers: This means "my universe" and suggests that the person is your whole world.
Informal:
* Tout pour moi: This means "everything for me" and is a common way to say "my everything" in a romantic context.
* Mon précieux: This literally means "my precious" and is a more playful and affectionate way to say "my everything".
Other options:
* Ma vie: This simply means "my life" but can also be used to mean "my everything" depending on the context.
* Mon amour: This means "my love" and is often used to refer to a romantic partner.
Ultimately, the best way to say "my everything" in French depends on the situation and the relationship between the speaker and the listener.