What is the best procedure to tighten my lower face/jaw and double chin? (photo)

You have the option of less invasive skin tightening with Sofwave which is an Ultrasound based device. It helps with tightening the jowls and neck. There is no downtime.
The other option is to do a mini facelift.
Regards
Dr. J

If you wish to go nonsurgical, you should consult with an experienced, board certified cosmetic dermatologist filler expert to discuss the use of various robust HA fillers to achieve your goals.
For example, consider the use of a robust, HA lifting filler cheek augmentation to lift the cheeks, create a more feminine Ogee Curve, oval, heart-shaped face; consider a robust HA contouring filler for enhancing the lower third of the face and straightening and defining the jawline (which, in itself, would secondarily help to tighten the submental region).
Both approaches can be performed in experienced hands in about thirty minutes, with immediate results and little to no significant post-treatment downtime.
Exercise a great deal of buyer beware caution when being hawked this or that expensive, supposedly "next big thing" laser or RF gizmo, since the hard science to support the use of these devices lags well behind the heavy marketing and social media hype to promote them.
Hope this helps and best of luck.