I've read that the rear springs make the biggest difference in ride on our cars. Any progressive rate springs (Hotchkis-Intrax) would probably be comfortable.
I've had ST springs on my car all around and the ride was a bit rough but I didn't care. Then I swapped the rears to Intraxx because I was tired of the rear springs popping out whenever I jacked the car up (front or back)so I replaced the rears with Intraxx springs and kept the ST rears in my garage.
The ride was so much better and so much more comfortable that I sold the ST rears after about a month. Showed me how big of a difference in ride progressive springs make