Severe Diastasis Recti - What is the best treatment? Mesh? Ventral Hernia? (photos)

You appear to have a significant rectus diastasis in addition to some excess skin.  Diastasis (unlike a true hernia) is not covered by insurance.  A diastasis may be able to be corrected in the traditional manner with suture plication (tightening), however in certain cases, if the abdominal tissue is weak/connective tissue disease, a mesh may need to be used to reinforce the abdominal wall.  If your tissues are inherently weak, even if you plicate aggressively, the results will tend to be short lived and a recurrence is likely (mesh doesn't stretch).  This determination is best made by your surgeon.

You definitely have a weakness of your abdominal wall fascia and a seperation of the rectus muscles of you abdomen. You need a thorough physical exam to evaluate the possibility of a hernia. Maybe even a CT scan. Having said that, you are definitely not alone. Mothers may develope all types of "baby bulges" after child birth. Some women may have multiple pregnancies and maintain a flat washboard abdomen, and others have one child and have an extensive weakness similar to yours. 
Unless you truely have some type of connective tissue disorder, which you should have evaluated by a rheumatologist, then you need a tummy tuck. Depending on the intraoperative findings , I dont think a mesh will be of any help in treating your probable diastasis. An in person consultation is needed to give you the best recommendation. Find a board certified plastic surgeon with experience treating hernias and complicated abdominal wall  reconstructions. Best Wishes