Mattress thickness will depend on the number of layers in the bed. Quality hybrids have multiple layers, all of which are at least a couple of inches thick. In addition to the 2-inch or more comfort layer, the transition layer will likely be a couple of inches. The pocketed coil layer is typically around 6 inches thick, while the base layer is around an inch. All that means your hybrid should be at least 10 inches thick. A high-quality hybrid should also have a coil support layer that constitutes at least half its total thickness (i.e. if the mattress is 12 inches thick, then the coils should be 6 inches or more).