I need more definition to my long, narrow face - How?

I would like to have a more defined jawline, as mine's very weak. If I gain only a couple of kilos(my BMI has always been around 18, so I'm slim), you can immediately see it on my face(double chin-ish). I also feel like I need more cheek volume - when smiling it seems like I have much volume and I get these less flattering nasolabial folds, but when face is resting, it's just long, narrow, flat and hollow. What procedures should I look into?

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