Covering chimney opening with Plasterboard?

I have recently taking out an old fireplace in my bedroom leaving a big gaping hole in the of the wall. I thought I would have to brick this all up and then plaster over to bring it back in line with the rest of the wall. A friend has recently said I dont have to do that, just remove all the old bricks, rumble and dust and cut some plasterboard to size, stick with sealent then skim over with plaster. This way seems quicker and cheaper, but is it ok or even safe to do? I will be putting wallpaper up also. I am just worried my bed might cause the plasterboard to crack, as my bed will be leaning against the of the wall.