How do I describe the difference between these two fabrics?

I have some very comfy short cotton nightgowns whose basic fabric feels pretty much like a T-shirt. After years of use they are wearing out. When I have tried to buy more by ordering online, it keeps turning out that the fabric (which sounds the same by description) is mushy like a baby’s sleeper, and I do not like it. What is the difference in how they are made? What do I have to know to avoid those soft-soft-soft cottons and get the slightly firmer T-shirt fabric? (If it’s a matter of woven vs. knit, I confess I can’t tell the difference.)

I have looked in many stores (where I can touch the fabric for myself), and all I can find that way is the super-soft mushy stuff.