How far is it from the rail to the ground level? If it is a high bridge, a deck girder might look good. In your earlier diagrams, the bridge looks to cross a road and a river. I think a 2 or 3-span bridge would look good here. Theoretically, you could have a main span and approach spans, but that may be too complicated for its length. A low-sided bridge would make the trains more visible and could be a cool place to show off locomotives and rolling stock. Prototype curved bridges are made up of multiple straight spans joined at an angle. Curved spans could buckle under load as the weight isn't on the chord between the supports. The deck and rails are of course still curved but the load-bearing components are linear. You might be able to kitbash a bridge from Walthers or Micro Engineering kits or you may have to scratchbuild. The Micro Engineering viaduct kit may be a good place to start. I have seen photos of people make curved bridges out of that kit before. Or check out Kibri bridges too. I think they have a curved bridge kit.