The size of your breasts at 8 months should be rather close to the size they will be 8 weeks postpartum when Your whole body has learned to control its milk source.
If you prefer an correct sizing for nursing bras, https://miriamnhiy577665.verybigblog.com/29255823/an-unbiased-view-of-when-is-the-best-time-to-buy-nursing-bras