You have to first figure out how the client would ship and then find logic that mimics it. What would actually happen if someone ordered a large bed and two large lamps? They need to define that first and then you could try to add logic to the site to mimic that.
Do they ship items separately using different carriers? Do they combine the items into one larger package and make a single shipment? First thing is first, clearly define how they do it and then you can see if you can figure out logic that mimics their decision process when shipping.