18 Model S - 21" vs 19" wheels comfort

I bought the car used and I'm pretty underwhelmed by the comfort level as I had expected way more of a "new" sedan with air suspension. Anyone with valuable input on the difference in ride comfort from 19s to 21s? What bugs me most is that our pretty uneven roads gives a very hard bumpy feel. I do not care about the looks and if I get cheaper tires, longer range and don't destroy the comfort (at least I suspect the 35 low sidewall tires are the fault) then I'll swap out the 21s in a heartbeat.