The phrase "You're good" is already standard English.

However, depending on the context, you might want to be more specific. Here are a few options, depending on what you want to say:

• To acknowledge someone's skill or ability: "You are good at that." / "You're skilled." / "You're talented."
• To reassure someone: "You're okay." / "You are alright." / "You're doing fine."
• To decline an offer: "I'm alright, thank you." / "I'm fine, thank you." / "I'm good, thanks."
• To compliment someone's character: "You are a good person." / "You're a good soul." / "You're kind."