Uno has asthma and I just use the Pet Gold litter that you can refill the big 30 lb. buckets with at Petco, it is pretty cheap and he has not had any problems with the litter. I have noticed that about every 4th time I refill the bucket it seems to be more dusty and smaller granules but still no problems.
If you don't mind my asking what are you treating your kitty with for the asthma, maybe there is a better way of treating it so he does not have as many flare ups. I hardly ever have trouble now with Uno and asthma, it seems to have gotten better over the last 6-9 months and I hardly do anything as far as treatment, but I know there are lots of options out there. When he does have an attack I use the Aero Kat inhaler with either the steroid inhaler if it is really bad, or I use the Albuterol inhaler if it is a mild attack. If he refuses to let me do that then a few days of Prednisone clears him right up and he is good to go for another few months. Currently he is going on almost 6 months asthma free!