Never thought it would be necessary until Sydney is surrounded by bush fire, now!
I am wondering what purifiers are decent. Do not know much abut air purifiers. Please use Xiaomi's as a benchmark, if possible. BTW, Xiaomi's ebay official shop doesnt sell the air purifiers. Maybe they have been sold out.
I'm in the same boat - I know that getting a HEPA filter is important… https://www.kogan.com/au/buy/kogan-smarterhome-smart-air-pur… might be OK?