For inner-spring, 10-12" is standard. It includes springs + layers of cushion. The 13-14"+ mattresses are typically an inner-spring mattress with extra layers of foam....sometimes memory foam to make it a hybrid.
If it's a memory foam mattress, the springs are replaced by a base layer of foam and depending on density, can be thicker or thinner than 10-12".
In my experience, mattresses less than 10-12" are going to be flimsier these days, but you don't gain a lot by going thicker than that. I'm 6'4", 230+lbs....so I prefer a mattress that can support me and won't end up with a divot in the middle after a few years.