
By the way, mattresses are not subject to legal regulation besides infant mattresses for cribs. The reason mattresses only come in a few different sizes is because it is economically efficient for companies to produce them in the same factories as their competitors or, if they own the factory, using equipment that is also used in competitors' factories.
A body of originalist scholarship has suggested that "regulate" means "to make regular". A "well-regulated militia" is therefore one that has standards and functions efficiently. Regulation of interstate commerce is likewise what happens when laws are passed to standardize commerce and make it flow without state-interstate barriers.