Good day girls, after my first childbirth I breastfed for six months, …

Good day girls, after my first childbirth I breastfed for six months, then got pregnant again. And even after breastfeeding, my chest is still saggy, like that of women in their sixties. Not at all firm, thought that when milk accumulated during pregnancy, the breasts should swell and regain firmness. But no, it's still like with grandmothers. Can anyone who has experienced this situation tell me what they did? Maybe they trained their breasts for firmness?