So, you say your ideal is a wagon, but you list preferred body styles are coupe or sedan. My inclination is to recommend a 5 door.
With you wish list for A/C seats, I'm thinking a higher end make might be of interest, Audi A3 comes to mind, but repairs can be a bit expensive (relability reports here have this model "average").
I rented a Golf 5 Door on vacation recently and liked it quite a bit. I'm not sure what they have for high end amenities. Another well reviewed vehicle is the new Ford Focus ST, but probably not something you're going to find for <$20K given they are 2013 model year or newer. Cars.com shows a couple at $21K so if you're really good at bargaining maybe.
The other one that I think fits in this group would be a Mazada3 (possibly the Mazadaspeed3)