First thing I would do would be to get a cheap, (like $3 or less), plastic painting dropcloth and wrap the mattress up. Then put the fitted sheet over it so no more fiberglass or anything else can get in the room from the mattress. This will prevent the fiberglass from multiplying.
Put on a face mask, and start vacuuming up every surface in the room. Almost every vacuum cleaner, even the upright ones, has an inlet where you can insert a hose with an attachment to clean walls, curtains, etc. If your vacuum cleaner doesn't have a hose or attachment, frequently a vacuum cleaner store will have them in various sizes. I think Singer still has stores in malls, not sure.
Finally, at the end of it all, spray some water mist into the air so it will cause whatever dust is floating around to come to the floor and then vacuum that up. That's on old trick people spray painting cars use before they start.
That ought to do it.