Impressions of seat comfort vary greatly, partly because people differ in size and shape. Given how hard it is to evaluate long-distance seat comfort in a brief test drive, I'd try to rent or otherwise drive some candidates for an entire day. Some large used car chains like Carmax might provide a one-to-two-day trial. If so, you might be able to thoroughly evaluate a few different cars.
The Camry could be a good choice. For maximum fuel economy, you might be able to find a Camry Hybrid in your price range.
A 2006-2012 Ford Fusion might also serve you well. The 2010 has had issues with the throttle body, but these might have been resolved by a recall. Reliability has been iffy for the 2013 and up.
The Buick Verano is a smaller sedan, but is very quiet and has comfortable seats. Reliability has been very good so far, but the oldest ones are only three years old. So this could potentially change.
The related Chevrolet Cruze is almost as quiet and gets significantly better fuel economy, but its reliability record has not been as good.
If you're willing to drive a car with a manual transmission, I like the Ford Focus. Otherwise I don't trust the reliability of its automatic. Fairly quiet with (in my opinion) very good seats.
Finally, Lexus only offered the HS 250h sedan for a couple of years, so they might be hard to find. But reliability, fuel economy, comfort, and quietness should be good.