Hi minmin001,
While 2 of the 3 layers are probably good quality (although they don’t describe the middle layer in terms of exactly what it is or other information such as softness/firmness that would be useful) … I would be very wary of purchasing a mattress that used more than 1" of 3 lb memory foam (see the memory foam guidelines I use here) unless you are in the very lowest budget range.
I would also be very cautious about buying any mattress from a big box store because they know little about their mattresses or how to help you make a suitable choice in terms or PPP (Posture and alignment, Pressure relief, and Personal Preferences) and the suitability of a mattress for your body type, sleeping positions, preferences, and physiology is just as important as it’s quality and value. If you make the wrong comfort or support choice … then a mattress would have little value to you regardless of its quality or value in “commodity” terms. You can read more of my thoughts about buying from a big box store in post #4 here. In essence … you are rolling the dice and hoping your number comes up.
Phoenix