Weighted Blankets can be very pricey - DIY is possible but what if you don't know how to sew? Here's a blog post about a "NO SEW" weighted blanket. I would use a different filler, but still think it's very doable.
When the child is awake, drape it across his lap or around his shoulders. The deep pressure touch stimulation brought about by the blanket will produce serotonin in the child, which is a hormone that will help to calm him down and produce a happier frame of mind.