what is the best type of Air purifier to buy?

My 2 1/2 year old has asthma. So i need to buy a purifier for the room. Which one is the best kind? And I heard the Ozone kind are suppose to be bad for you, so I want to make sure I don’t buy one of those. Please tell me your experience.
How about Sunbeam air cleaners. Has anyone ever heard of them? My husband has a really old one and says it will work find, but I don’t know. I can’t even find the model online.