Here is how I lower the hammer. Pinch the tang of the hammer with the thumb and forefinger of your weak hand. If right handed, you reach across the back strap with your thumb closest to your body and your forefinger away from your body. Back of left hand pointing toward the muzzle. Pinch the hammer firmly and pull the trigger lowering the hammer. I've tried the thumb roll method but pinching works best for me.
An extended mag release is also helpful, as well as, better sights.