My kid has horrible problems with mold and dust, we've used a Shark HEPA fan in his room for several years and he's been doing very well every since. The filter is about the size of a normal HVAC filter, and you can get ones that filter odor as well (has a charcoal membrane). Our Dyson HEPA fan doesn't come close to the Shark.

A good filtering fan will pick up the dust that's kicked up into the air, but to reduce that dust you need to clean and vacuum like a madman, replace your HVAC filter regularly, clean the vents/ceiling fan/all flat surfaces, and make sure your air returns arent blocked and functioning.

Also consider a humidifier or HVAC humidifier. In the winter our humidifier works on the whole house and helps with congestion quite a bit.