Purchase a mattress bag for your king size mattress. Some local shipping companies, such as U-Haul, sell the bags. For online bulk purchases, OurShippingSupplies.com has mattress bags for sale in bulk.
Get a mattress box if you are shipping the mattress a long way or if you are using a moving company that requires the king size mattress to be in a box. Eco Box sells king size mattress boxes on their website.
Put your king size mattress in the mattress bag for shipping. Peel off the adhesive cover to seal the end of the mattress bag.
Slide the bagged mattress into the mattress box, if you are using it. Some shipping companies require a mattress to be boxed instead of just placed in a mattress bag. Use packing tape to seal the ends of the mattress box.
Apply a label with your name and address on the mattress bag if you are not using the box, or on the outside of the box.
Contact a shipping company to pick up and ship the king size mattress. Some shippers, such as Transit Systems, specialize in shipping mattresses nationwide. Get a quote and set a date for pickup of the mattress.