When is it safe to bring found furniture inside (concerned about bed bugs)?

I found an adorable foot stool on the curb in my area. It is mostly metal with a thick cushioned top that is heavily stapled to the frame. After lightly cleaning it, I have covered it in thick plastic and stored it on my balcony for the past 4 weeks, where temperatures are minus zero almost daily. Question: when is it safe to bring it inside? Next question, is there a product that I could buy to treat it with that you have used and would reccommend to prevent an evil bed bug infestation, if in fact any exist and have survived the cold?

Many thanks!