You can create the bed (or whatever) as a cloth prop and then lower the person on to the bed and animate the cloth. If the settings are right on the cloth then it will depress where the body touches. Then render the frame you wish to use. I kinda did this in a picture in my gallery where the cloth comes down over the person, but in this case you will ned the person coming down on the cloth. Tricky.. I might give this a go tonight ^_^