Heel and toeing and double declutching are completely different. With double declutching you bring the clutch up when the gear lever is in the neutral position and then blip the throttle, press the clutch down again and select the gear. Heal and toeing is as described and allows braking whilst blipping the throttle. It is possible to heal and toe and double declutch at the same time.
A couple of things with heal and toeing, the car ideally needs a firm brake pedal to give the foot something to pivot off (Renaults with massively over servoed brakes are tricky) and the engine should resond promptly to having the throttle blipped.
