We had Sunshine install a Carrier Infinity Air Purifier.
Infinity Air Purifier GAPAB | Carrier – Home Comfort
My wife is sensitive to dust and pollen and it help a lot.
When Sunshine installed it they went up into the attic and sealed all the joints in the air ducts so that dust wouldn't leak in through them.
The unit itself is a MERV 15 air filter which is about as high as you can go. It has a thick filter and also does electronic zapping to kill germs.
Downside is the filter are expansive, about $60 installed. But the results for us are worth it. We change the filter every 6 months.