You probably know what I'm going to say. Steel. Bike.
Steel is one smooth ride. Check out - Surly LHT, Surly Pacer, Surly Cross Check, Trek 520, Jamis Aurora, Jamis Quest, Jamis Satellite, Jamis Eclipse, Raleigh Clubman, Raleigh Sojourn, Specialized Allez Steel Double, etc, etc. Or any steel framed bike. (Maybe a used Mixte if you're into those.) A touring bike would have a less aggressive posture. Jamis Auroras have an adjustable height stem. So you can ride more upright if you like. Well, I wish you luck.

(You could always upgrade any of these to your specs.)