Custom mattresses fall into two specific categories: one type is made individually to order, customized to your unique specifications. The other is one you can customize in your own bedroom, because it provides different settings for firmness, positioning, and so on. Adjustable beds and quality air beds like Sleep Comfort, and Natural Form fall into this category.
Other mattresses have “custom” in the name (such as Custom Comfort) but in fact do not offer customizable mattresses either in factory or in house. They just use the name to make it sound like a good mattress.