Slimmer Nose with More Height Through Fillers?

Unfortunately, generally fillers do not do a very good job reshaping the tip.  Fillers are best used to fill depressions and do limited adjustments to the bridge and profile.

Every technique has its value. And the improvement varies between areas. With tissue fillers, the nasal bridge is well treated, so is small areas of asymmetry and irregularity. However the nasal tip isn't at the top of the list. There can be improvement, but by the very nature of the product; its a soft gel, the degree of definition is limited. Plus its an area that hurts more than the bridge. So more pain, less gain. My advice is you're better of with a surgical rhinoplasty. But please choose your surgeon with care. You don't want to find you're needing injections after wards for surgical irregularities.

Great question.
Unfortunately, In my hands, surgical rhinoplasty is the treatment of choice to get narrowing and definition of a wide, flat, African American nose. Even surgery is a bit unpredictable since some noses have very thick skin, and weak soft cartilage.
You should go for a consultation with a board certified facial plastic surgeon with experience, and lots of photos of noses that resemble yours.
I hope this helps, and best regards.