Hi Mic,
As you probably know SleepEZ is also one of the members here and they would also make a great choice. There are also other companies that do this and the tutorial post also includes this link to a list of the members here that sell mattresses online and many of them also make component mattresses with zip covers that have one or more exchangeable layers in a range of different designs, options, types of latex, and price ranges for those who like the feel and performance of latex.
No … it’s not necessary to buy them together at all and I would treat them as separate purchases (although you may choose to do so if the retailer or manufacturer where you buy your mattress also has good value for their adjustables).
Phoenix