Assuming you don't want to post-process all your DOF needs, here's how to achieve shallow depth of field optically:
f/2.8 isn't large enough unless the focused and non-focused area are farther apart than I see in this picture. For a human body to both in and out of focus, I would go at least to f/1.8, and 1.4 if you can.
Wide angle lenses won't work too well. Although a tele lens in needed, the factor that really determines DOF is the ratio of how far away the out of focus are is to the focused area, relative to the ratio of the how far away the focused are is to the lens. In other words, if you're 200 feet away from the in focus subject, and the intended defocus are is only 2 feet, it won't be very much out of focus--that's only 1%. However, if you're much closer, like 10 feet away from the focused area, the intended defocus area still 2 feet, that's fully 20%. That should really throw the background out of focus, especially with a f/1.4 lens.
Given the environment in this pic, 50mm, which has the same field of view as a 75mm lens on a cropped sensor, could work fine if you're 8-12 feet away. Bottom line, get as close as you can without resorting to wide angles and try to fill the frame.
Shutter speed doesn't have anything to do with DOF whatsoever. But obviously it's important for proper exposure, which is always fundamental.v
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