Hi Nemix,
All the layers and components in a mattress will affect the “feel” and performance of all the other layers both above and below it so what you feel on a mattress is a combination of the “feel” and firmness and properties of all the layers … not just specific layers or components so any mattress that uses a different combination of materials and components will be different from another mattress.
All the layers and components of a mattress compress simultaneously (one doesn’t start compressing when the ones above it are “finished” compressing) but they each compress to a different degree or percentage of their thickness based on their firmness level, thickness, what is above them, and how deep they are inside the mattress. Softer layers compress more than firmer layers, thicker layers compress more than thinner layers, all layers compress less when there are thicker or firmer layers above them, and upper layers compress more than deeper layers.
There is also more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support” and “pressure relief” and “feel”.
Assuming that the materials in a mattress you are considering are durable enough for your body type and meet the quality/durability guidelines here … the choice between different types and combinations of materials and components or different types of mattresses are more of a preference and a budget choice than a “better/worse” choice (see this article).
Either one will be strong enough but of course I would make sure that the foundation you use on top of the steel bedframe is suitable for your mattress.
Phoenix