My skin is stretched and thin.Internal bra or mesh for large implants - will this help to avoid bottoming out or early sagging?

Unfortunately, you have not provided photographs or told us your bra size. 450 cc implants weigh 1 lb. each, will descend inferiorly and laterally and make your situation even worse. The most important thing is the lift. I recommend The Bellesoma Method. This will reshape your breast tissue creating upper pole fullness without implants, elevate them higher on the chest wall and more medial to increase your cleavage. Vertical scars are avoided and nipple sensation (in 95%) is maintained. Later, fat transfers or small implants can be placed if additional volume is desired.

Best Wishes,

Gary Horndeski, M.D.