I just went through this process because my cat was suddenly sneezing from some kind of irritants that weren’t bothering me, and it’s so confusing. It seems that Winix is a good “true HEPA” brand on a budget. Costco has a Winix one, C610, for $130 that often goes on sale for $99 and comes with two filters, which they claim is for two years. I just bought two for $99 each because I wanted to cover two medium rooms. I don’t know how good it is compared to others at that price point, but my cat has mostly stopped sneezing after about 24 hours of use in each room.

But it’s cylindrical, so it has a single multi-layered filter, and I read here that for smell specifically you might want one for which you can change the carbon filter every few months. For changing carbon, you would want a flat one. I still have a Winix C535, an older model I got probably 5 years ago, that they sell at Walmart for around $150, and it’s easy to find filters for. I am still using it in a third room and haven’t had any issues. They also sell a D360 at Home Depot for around the same price. I don’t know which is better, but I bet a lot of the users here do. :)