May I recommend something a little different that will totally connect with him at an 18 month level AND will give you some more freedom?

www.ergobabycarrier.com/

You can get them cheaper on eBay or other consignment sites if the price is hefty. I can carry a 5 year old and not feel them on my back, despite having a bad back. And, this is what I always resort to when I've got a regressing toddler/preschooler who is clingy and scared to be away from me. And, I'm not even talking about a child who came into the home with issues. Its just been my experience that the physical contact helps a LOT of the issues you are describing.