The correct heel-to-toe drop depends on what’s comfortable for you. Most shoes have a heel drop of between 4 and 8 mm, with 12 mm being the largest that you can find easily.
12 mm may place extra stress on the ball of the foot. Between 4 and 8 mm is ideal as it takes the strain off the ball of the foot and the Achilles tendon, allowing you to walk without pain and transfer energy efficiently for a powerful toe-off.