Hi CT29,
It depends on each person’s body type, sleeping style, preferences, and individual perceptions and physiology. As a base layer it would probably be fine for most people but it may not have enough thickness to provide the combination of pressure relief and alignment that is necessary for a particular person by itself. The only way to know with reasonable certainty is to either test it carefully and objectively or to sleep on it for a period of time. Post #14 here has more information about how thinner layers will compress and get firmer faster than thicker layers and mattresses and may be less adaptable for higher weights and different sleeping positions. All the layers and components of a sleeping system interact together so the choice of what topper may be best for you would depend on how the mattress underneath it interacts with both you and the topper. The better quality the foam in the mattress … the more “adaptable” and the greater range from soft to firm it will have by itself.
My personal tendency would be to test the mattress and topper together (so you can experience exactly how they perform and interact together) and then just the mattress without a topper and then choose the one that provides the best PPP (Pressure relief, Posture and alignment, and Personal preferences).
If you did decide on just the mattress … then I would make sure you sleep on it for a while to give it a chance to break in and for you to go through the initial adjustment period that is part of any change in a sleeping surface and then decide whether you need a topper based on your actual experneince. The topper guidelines in post #2 here may be helpful if you do decide you need to add a topper to any mattress.
Phoenix