Is your CZ a CZ-75 or a CZ-75B? The CZ-75B (The type I own) contrary to the advice of Superdown has a firing pin Block safety. It is designed to safely carry a round in the chamber ready to go. It makes no sense to me to carry the CZ-75B cocked and locked although you can under certain tactical situations and is still safe (unless while holstered you accidentally swipe it down and there you are... ready to blow your family jewels off if you then accidentally swipe the trigger (Murfy's Law)- This option of carry gives me the creeps! The CZ-75 doesn't have the block, although I consider it safe to carry it with a round in the chamber. As long as you don't drop it from a hundred feet up on concrete and it lands just at the right angle for the firing pin to come down and contact the primer of the cartridge. Note: The firing pin block safety is often time called an inertial firing pin block (CZ-75B).
As for lowering the the hammer? It is similar to lowering the hammer on a revolver. Practice with an UNLOADED CZ-75 and it will become second nature. If this still gives you the creeps use your other hand and grab the hammer with your thumb and index finger, and with the other hand on the trigger and do it, always pointing in a safe direction. The CZ-75 is one of the best pistols in the work. To be honest, decockers gave me the creeps more than a single/double action. That snap during decock...whoa. Although my SIG-226 I carry for duty has one I honestly say that I like the CZ-75B better. Practice!