None! Unfortunately, lots of home remedies and clinical studies have shown that the only way to tighten loose skin after childbirth is eating right and getting back into shape. The natural collagen in the skin intended to stretch for the pregnancy is designed to tighten (contract) after childbirth, but, for some women, this doesn't always happen.
None. Exercise will not tighten your skin. Muscle tone will improve though. The skin will improve by itself over the next 6 months. Good luck from nyc.