That's tough, small cars aren't known for being quiet. That said, I'll second the Mazda 3. I'm not really a fan of Mazdas but I rented one of those for a 1600 mile road trip and I was very impressed with it's blend of comfort, quiet, pep and fuel economy. Also how well it got me to the cabin down 18 miles of dirt, gravel, and a bit of snow. If I had to buy a car that'd be towards the top of my list.
Another option is to give yourself (and/or your dad) a project to make whatever car you get as quiet as you want. Look into how car audiophiles do it. You can get as intense as you want, including taking out the car seats to add dampening material to the floor, taking off the door panels to do behind those (biggest return on effort), or coating the wheel wells to remove tire noise. You can do all the above in a weekend, but it's definitely a project. But you can make any car as quiet as a 700 series BMW, which for a long time was the gold standard on quiet rides.