The deep support within a mattress (from the innerspring unit, latex core or polyurethane foam support core) is primarily concerned with helping maintain a good alignment and the prevention of bottoming out, and can be quite independent of the overall surface comfort. People often mistake a “firm” mattress as something that is “hard”, so be sure to differentiate between support and surface comfort. I prefer to refer to support units as “firm or strong”, but surface comforts as “plush” or “hard”. I try not to confuse the nomenclature by using “firm” to describe both the innerspring unit and a level of surface comfort. In general, there aren’t too many times that you’d want to recommend a mattress that has poor support, as good neutral alignment is one of the key predictors of the time spent in deeper phases of sleep.
Knowing the difference between the strengths of the more common innerspring units is important, as you’ll want to match that to the needs of your customers. Does someone need more contouring support or have a larger differential between their shoulders, waist and hips? Then maybe a marshall spring unit would be appropriate. Are they very large? Perhaps a very sturdy knotted offset spring might work. Do they need good support but less conformation? Perhaps an open-ended sensory arm spring would be more appropriate. While the comfort layers of a mattress mostly determine the overall comfort, the support unit will have a contribution, which is why it is so important to be familiar with the different offerings and their best applications.