Hi sunbird,
Different types of mattresses will have different levels of “rigidity” depending a lot on the materials that are inside them … especially the support system. The glover park has a pocket coil that is surrounded with a foam border and has polyfoam on top and it’s completely normal that this type of design is “floppy” … especially in a king size. Other types of innersprings where the individual coils are attached to each other with helical wire or that have a border rod that doesn’t bend as easily are much more “rigid” and can stand on their sides. This has nothing to do with the firmness of the mattress when you lie on it but is just a normal part of any mattress that has these types of components.
A latex mattress for example would be even more floppy even in it’s firmest versions and is like carrying a very heavy bag of firm jello (it would be even heavier and floppier than the mattress you have).
This is completely normal for this type of mattress and has nothing to do with its ability to hold its shape.
Consumer reports is one of the “worst” mattress reports that I’ve ever seen and they do an incredibly poor job helping consumers make an informed mattress choice (see this video and this thread for more about CR).
Phoenix