We left the two twin beds in place. Removed the nightstand drawer. Then bridged the space between the twins with five planks. The planks are made with 3/16" aluminum Z metal brackets and 3/4" plywood. A commercial storefront contractor bent the Z metal for us. Then we ordered three small custom mattresses(sort of like cushion) for in between the twin mattresses. We use a very cushy down comforter as a mattress topper and, walla!, a super comfy bed. Total cost, $800, mostly because of the custom mattresses.
The whole conversion creates a king size bed/great lounge area. It also lets us change back to twins really easily. We are quite pleased with ourselves.
The con is that it makes the drawers under the beds a pain to get into.