It's really surprising to me that mattresses larger than a king/cal king are not more common. When I was single and sleeping on a full size mattress, that felt pretty good. Now that I have a partner and we upgraded to a king, I actually have LESS space since there are two of us sleeping in a bigger mattress. A king split between two people means that each person has the width of a twin size mattress. In my opinion, this is entirely inadequate and is a massive downgrade to me. A full size mattress is 54" wide, so for each person to get the equivalent of a full, you'd need a mattress that's 108" wide (Alaskan King size.)