Formal:
* Vá dormir: This is the most formal and direct way to say "go to sleep."
* Durma: This is a more polite and respectful way to say "go to sleep."
Informal:
* Vai dormir: This is a more casual and friendly way to say "go to sleep."
* Dorme: This is a more relaxed and familiar way to say "go to sleep."
Other options:
* Boa noite! (Good night!) This is a common phrase used to say goodbye before going to sleep.
* Durma bem! (Sleep well!) This is a polite way to wish someone a good night's sleep.
The best way to say "go to sleep" in Portuguese depends on the context and your relationship with the person you are speaking to.