Hi there -- Thanks for your question. As a very broad generalization, thickness certainly can affect the softness -- speaking very generally, a thinner mattress will typically have less softness. However, this is not really the case with PlushBeds. They actually publish the ILD of each of their models, so that you know exactly how soft they will be.

ILD is determined using a machine that determines how much force is required to compress the material by a certain amount (say, 25%). So, higher ILD's mean that more force was required (i.e., the material is firmer) and lower ILD's mean that less force was required (i.e., the material is softer).

So, going back to PlushBeds, the Medium version of the 6" Natural Bliss model has an ILD of 24-26, which is the exact same ILD as the Medium version of the 8" model. So basically, each model is available in your choice of several softness levels and several thicknesses. But when you select a given softness, it should feel roughly the same regardless of which thickness you choose.

The only other factor to be aware of on this front is weight. A heavier person does run the risk of "bottoming out" on a thinner mattress, which will make the mattress feel firmer to that person than it does to a lighter person. So, for example, we would generally not recommend the 6" version for heavier sleepers.

I hope that helps.