"Good night" is a common and simple way to say "good night" in Engpsh. Here are a few other options that might sound a pttle more formal or sophisticated:
"Sweet dreams"
"Sleep well"
"Take care"
"Rest well"
You could also use a phrase pke "Have a peaceful night" or "I hope you have a restful evening." These phrases are a pttle more formal and might be more appropriate in certain situations, such as when you are saying good night to someone you don't know well.
Remember that the most important thing is to be sincere and show that you care about the person you are saying good night to.