Hi Strumbelina,
Their description seems to indicate the same thing but of course they would know much more about their own mattresses than I do. It’s amazing to many people how much of a difference a single layer can make.
This “dipping” sensation or the compression of the surface layers and the “cradle” that it makes is part of how a mattress relieves pressure. Different types of materials compress differently from each other and the firmness of the support layers also helps determine the depth of the pressure relieving cradle as well and how far “down” into the mattress your heavier areas will sink. It may be that you need a little firmer support layer (or a little thinner comfort layer) so that you still sink into the comfort layers enough to relieve pressure but your hips are “stopped” from sinking down a little sooner. In the most basic of terms … mattresses are always a balance between the “feel” and softness of the comfort layers along with the “feel” and firmness of the support layers. Inside this basic idea there are almost infinite ways to change how each mattress feels and performs using different combinations. the goal is always to let your body tell you which combination of materials produces the best possible PPP (Pressure relief, Posture and alignment, and Personal preferences) because mattress design can be far too complex to go by the “theory” of mattress design alone.
I would personally avoid choosing a mattress that you thought would need a topper and get as close as you possiblye can with the options you have in the store. Choosing a topper where you haven’t tested it in combination with the mattress you have can be as confusing and frustrating sometimes as choosing a mattress.
The more objectively you can test for your specific needs and preferences in the store … the better off you will be and the less fine tuning you will need to do after you have purchased or exchanged a mattress.
Phoenix