What procedure would help me achieve a more defined jaw line and chin? (photo)

Thank you for posting your question here!Let me start by saying that my answer is based on the limited information and pictures presented, for a more bespoke plan please consult with a plastic surgeon in person.
There are many ways to assess wether a chin is recessed and needs more projection , that involves many measurements including assessing the projection relative to other facial proportions (ex: the pogonion (most projected part of the front part of the chin) should be 3mm behind the nose-lip- chin plane), the nasal length should vertical chin length , the groove between the chin and the lower lip should be 4 mm deep ...etc but those are "ideal proportions" and do not necessarily mean that you have to have those proportions since traditionally they were based on the beauty ideals for a caucasian female which might not be applicable to everyone. that being said if this issue is bothering you and you wish to have that addressed you have many options.
1- you are right in mentioning filler, filler can be an option and it can give you reasonable results , yet you also mentioned some of the potential complications , from migration , reaction to the filler in the form of granulomas or even vascular occlusions that in addition to the fact that filler is temporary so if you want to proceed with this option you have to weigh in the risks and benefits.
2- Chin implants are also an option , they come in many shapes and sizes , and they don't necessarily have to look comical, if the right size and shape is chosen it can compliment your face. Implants can provide a more pronounced change. They do carry the risk of having complications that you should consider, including but not limited to malposition , infection . Bone resorption can occur but as long as the implant remains in place it is rarely ever noticeable, (medpor or similar implants tat integrate have less chances of causing that than silicone ones but they are a little more challenging to place).
3- For individuals with chins that are much more recessed, genioplasty can be an option, this involves moving part of the chin bone to a new position and plating it there , usually with the addition of bone graft. this gives a much more pronounced change though carries it's own risks and is a more involved surgery.
4- In certain individuals who's jaw occlusion is an issue and their bite is affected due to an under developed lower jaw/mandible that also results in a recessed chin then orthognathic surgery can be an option. Those surgeries are much more involved and lead to dramatic changes and usually fix the bite in addition to the recessed chin. Given how involved they are they carry the highest risk of complications.
That being said and based on the limited information provided I highly doubt that you will need option 3,4 , I would recommend that you consult with a plastic surgeon and discuss your goals and options with them so that they can come up with a plan that is tailored to your needs.

A small chin implant can accomplish augmenting your recessive chin forward for better facial balance, and proportions in addition to better structural support for the soft tissues in your neck. A surgical neck lift procedure can accomplish removal of the fat deposits above your platysma muscle with liposuction, surgical extraction of the fat deposits below the platysma muscle and a platysma plasty to significantly improve your jawline. A standalone chin implant can be done under local anesthesia, but the combination of a chin implant with a neck lift is performed under general anesthesia as an outpatient procedure.