Support Vs. Comfort
Support is how well the mattress pushes back against your body to keep your spine straight and promote good sleeping posture. Comfort is how the mattress feels in terms of soft or firm. Both soft and firm mattresses can be supportive, and the terms comfort and support are not opposites.
What's the Difference?
When shopping for a mattress, there are two things to consider: support and comfort. These terms are sometimes used interchangeably, and other times seem like opposites, but they are actually two separate concepts.
The level of support for a given mattress does not directly affect its comfort. A supportive mattress can have a firm comfort or a soft comfort, and firm and soft mattresses can have poor support. A term I often use to talk about support is "rigidity." Does the mattress keep your spine straight or does it sag in areas where most of your body weight is focused?
Comfort can be a tricky term, because you might be talking about firm comfort, soft comfort, or just "comfortable" in general. It is important to know that what is "comfortable" for one person might not be for another. So the term "comfort" should be used objectively in terms of softness or firmness.