Came across this:
http://www.archello.com/en/project/zeidler-residence-0/image-12
And it inspired me.....
Bit blotchy at the top of the shot.. Any suggestions?
Looking good - maybe bump up you shadow quality a little (around 2).
Different floor and Higher shadow quality
Ok, for my taste the floor now is a bit over saturated.
I attached a quick edit I did. The horizontal red line shows where your backplate horizon is on your image. I edited it such that it matches your scene. You can either edit the backplate or you can change your camera angle.
Also I suggest to use an indoor HDRI so that the reflection you get in the window isn't plane white, although if you got your back against a white wall while taking this "picture" it is possible .. if you prefer that, maybe add another painting over your image near the center in post and play with the transparency.
Thank you Philippe for your help.