Formal:
* Je suis à vous. (Literally "I am at your disposal") - This is the most formal way to say "I'm yours" and implies a sense of service or dedication.
* Je suis vôtre. (Literally "I am yours") - This is another formal option that carries a similar meaning to the previous one.
Informal:
* Je suis à toi. (Literally "I am yours" to a loved one) - This is a common way to say "I'm yours" to someone you are close to.
* Je t'appartiens. (Literally "I belong to you") - This is a more passionate way to say "I'm yours" that suggests a strong sense of love and commitment.
* Je suis tout à toi. (Literally "I am all yours") - This is a very romantic way to say "I'm yours" that emphasizes the total devotion of the speaker.
Other options:
* Tu me possèdes. (Literally "You possess me") - This is a more sensual and passionate way to say "I'm yours" that emphasizes the physical and emotional connection between two people.
* Tu es tout pour moi. (Literally "You are everything to me") - This is a romantic way to say "I'm yours" that expresses the importance of the person in the speaker's life.
The best way to say "I'm yours" in French depends on the specific context and your relationship with the person you are talking to.