I've got good news for you. Sort of. 18's with grand touring tires will make a phenomenal difference.
1. Tires. Eve if you stay with 19's, There are some that make a big difference, usually in the Grand Touring class. Check Tire Rack's reviews. From experience, Michelin Primacy MXM4 or Bridgestone Turanza Serenity Plus are as smooth as you can get, and both are still "driver's tires".
2. 18" wheels. I'm running the Turanza on OEM 18's. The ride is impressively smooth over every type of surface, especially potholes.
3. Standard (Non-sport) springs. If you do have the sport suspension, this will be a big improvement. Parts are cheap, but labor and alignment will run you $500-$750.
Too bad you're not in Houston. We could to a test swap of wheels and tires!
I'm thinking I can go firmer in one or more of the areas and still keep it smooth enough for me. Grass is always greener...