Eventhough the window sill is on the south side that room is on the cool side. I have a Miltoniopsis and many Phals on this window sill. These orchids are very healthy and seem to like their spot. A lace curtain filters the light.
My Sedirea joponica grows under conditions similar to what you describe, Danie. It is in an indoor greenhouse, but it gets plenty warm in there and there is lots of light. As long as you monitor the watering, I think it should be fine.