Would a sliding genioplasty or advancement of the maxillamandibular joint help? (Photo)

Thank you for sharing the photos. I can certainly appreciate your concerns regarding your lower face. Your mid and upper 1/3s however are excellent and I would personally advise you against MMO for cosmetic reasons. There is very little to be gained from that. You can simply have a genioplasty and effectively address all your concerns in your face. This is likely to result in dramatic cosmetic improvement and in my experience, this is also likely to improve your sleep apnea significantly (if the etiology of your OSA ie related to an abnormality of your tongue base/hypopharynx) . On the other hand, if you have severe OSA and your primary concern is to improve those symptoms (functional and not cosmetic) , the MMO is the surgery you should consider.

Hello,    Jaw surgery or a orthognatic surgery decision needs more anatomic information. Mild sleep apnea and mouth breathing does not sound good. You are so young and look normal weight. Those complaints may be related with your smal mandible. Your question is very hard to answer without a proper examination and CT scans. 
  Sliding genioplasty will only fulfill your aesthetic demands. You really have good projected frontal and cheeck bones, which is nice for you. But those features requires a strong chin for a better harmony. 
  After detailed consultation, If you don't have any anatomical and functional problems you may start with a jawline and midline chin filler injection. It is a good choise for you to gain time while you figure about your surgery type,clearly.  You need to be sure that your surgeon is a professional, exprienced and board certified facial plastic surgeon. 
Best Regards,

Because of your very strong cheekbones and forehead the chin recession/lower jaw shape looks out of proportion. Without any obvious bite issues orthognathic surgery is not indicated. The real question is whether a chin augmentation alone is adequate or whether the entire jawline needs to be augmented to bring the lower third into proportion. Only computer imaging can help answer that question.