Apart from the texture and feel, there is another very important facet of your mattress which influences your choice—the size.
Mattress Sizes and Dimensions Guide
They're similar in size, but the California king is 4 inches longr than the standard king while the king is 4 inches wider than the California king.
There are some oversized beds like the Alaskan king, Texas king, and Wyoming king, but they are way larger than the standard king and California king and are not easily found on the market.
The largest mattress size is an Alaskan king, which is 9 feet by 9 feet. To put that into perspective, a standard king size bed is closer to 6 feet by 7 feet.