Hi agims,
While I really don’t have a definitive guide on testing for pressure, as that is accomplished by you taking the time to test a product in person and your reaction after that activity, you may be referring to some of these posts:
Post #15 here talks about softness and pressure.
Post #2 here talks about the differences of firmnesses and the steps in the mattress shopping tutorial regarding what I call PPP (Posture and alignment, Pressure relief, and Personal preferences).
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”.
There are some general comments about the properties of an “ideal” mattress in post #4 here.
There is an article here about comfort and pressure relief.
I hope that helps. If not, let me know specifically what you had read and I’ll see if I can find it.
Phoenix