You don’t describe your lighting setup, but I think the bottom line is that you’ll need to greatly simplify your problem. You might need to composite the scene, and maybe use a combination of Cycles and BI techniques.
It seems to me that Cycles works by converging on a solution. Especially when you have a combination of high-key lighting and low-key objects, it doesn’t always converge … and adding more samples doesn’t help. (It simply “churns” around the same unacceptable-to-you solution.) Scenes that would be difficult to photograph on film, such as this one, seem to also cause problems for Cycles.
The solution I’ve found is similar: simplify the problem, and break it down into pieces that can be dealt with separately. For example, start with total darkness, turn off the sunlight, and light the interior-only scene using interior-only lights of appropriate colors. The solution ought to converge in 200 samples or less; less is better. Devise interior lights which emulate the color temperature and general fall of the sunlight. If the solution turns “noisy,” try a different tack.
Separately deal with the sun. Now the only thing that the sun actually needs to do is to throw slatted shadows on the edge of the window frame and perhaps on the bed. It does not actually have to light the interior scene.
Also consider that an identical effect upon the bed could also be achieved by a “gobo” on a conventional spotlight coming straight down onto the bed … composited into the finished image. (Ideally in such a way that you can fine-tune its color temperature without re-rendering anything.)
A deliberately higher-contrast setup might converge more quickly and more accurately. You can always de-saturate the image “in post.”
At the end of the day, what you need is an image that you could generate quickly, that you can now adjust and fine-tune quickly, and that looks visually plausible. There’s nothing in the play-book that says that to do that you must actually construct reality.
There are lots of real-world photo situations that are very difficult to solve “all at once,” but that can be broken down into a set of simpler, more easily-solved problems whose solutions can then be artistically combined. In some ways, Cycles is beguiling, because it suggests that “now at last we can solve the problem all-at-once!” when you really can’t.
It really helps to tag along with a studio photographer for a while, just to see the crazy tricks they do. For instance, I watched a group of photographers set up a “lovely springtime day scene” in a hotel lobby, with “sunlight” streaming in through the windows and so on. They did it at two o’clock in the morning on a moonless night.