Which procedure would produce natural and flattering results while targetting my long, weak chin and indentation? (photos)

To make quality assessment, we need quality information.
We do not make assessments of the chin without context to the rest of the face.
That said it appears you have some degree of micrognathia, mandibular hypoplasia or simply having been born with a slightly underdeveloped mandible.
If the body of the mandible is insufficient then formal jaw surgery may be indicated. This is complex and invokes changing your dental occlusion. If only the mentalis or chin region is insufficient then the chin can be augmented with a sliding genioplasty or implant augmentation.
To get a quality assessment I suggest having a few in person consultation with oral surgeons in your community. I think you will be better served by providers with oral surgery backgrounds than plastic surgeons unless the plastic surgeon had sufficient craniofacial surgery training.
Doctors from both backgrounds treat the condition but skill and experience may differ so consider having more than one consultations.
Best,
Mats Hagström MD