hi clara, and welcome to RP.
there's really not a lot more you can do with an image like this, unless you want to go artist on it. you've cleaned it up, done what you could to preserve the detail and made it look a lot better. i suppose you could bring out the traces and harness on the horse a little bit more, but aside from that, there's just little more detail to be had with that kind of image. one test you can run to prove out what i'm saying is to use a brightness/contrast adjustment layer and crank it up on brightness and some contrast. you'll soon see that there is no real detail to be had in the person, especially his face.
so, you've done fine. there has to be detail there in order to bring it out