Formal:
* Thriving: This emphasizes a state of growth and success.
* Flourishing: This suggests a strong and healthy state of being.
* Prospering: This is a more direct synonym, but less common in everyday speech.
* In a state of affluence: This specifically highlights wealth and abundance.
Informal:
* Doing well: This is a simple and common way to say someone is prosperous.
* Living the good life: This suggests a comfortable and enjoyable lifestyle.
* Rolling in it: This is a slang term that implies great wealth.
The best phrase to use will depend on the context and desired level of formality.