People with narrow heels have an excessive amount of lateral room inside the rear of their shoes. Some shoe stores sell adhesive pads to counter this problem however using these pads according to the manufacturers instructions may make a shoe too short for someone with a narrow heel. At work we cut the adhesive pad in two and place it on either side of the narrow heel. This takes up excess room where it exists without sacrificing the length someone's foot needs.
True moccasins have a continuous leather lace making those a good choice for the narrow heel. Clogs take your narrow heel out of the equation entirely making them an excellent footwear choice if your foot has enough volume to carry them. Boots that contain your entire foot generally work well for people with narrow heels and trim feet. Using the runner's tie can also snug up shoes around a narrow heel. Shoes can be too short yet still slip in the heel so focus on getting a good fit even if this feels unnatural at first.