Sizes depend on your individual body shape, existing breast tissue and also the width and shape of your rib.
Buy a bra in the size you want to be, then use rice sizers to the size of implant you’ve been offered and see what you get.
You might love the DD bra on your body – or you might not.
Try the sizers in the sizes your surgeon has offered you with a sports bra and then dresses and tops that you have – that will let you see how you look with that size of breast on your body.