Using a magnet on the bed might work. First, check to see if the top of the bed has enough polygons. Display>Document style> texture shaded. If you see a bunch of squares (or triangles) on the top of the bed, a magnet will work. You can change the display style back to texture shaded once you've checked.

make sure the bed is selected and then create a magnet. Adjust the location and size of the magnet zone so it roughly follows the shape of Ben and then move the magnet up or down to make the dent.

If the bed doesn't have enough polys to make the dent, you'll need to subdivide it (on the properties tab) and use a morph brush to make the dent. I think I remember you've used the morph brush before, but if you need instructions, ask.

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