Diet while breastfeeding

My baby is 5 months old and honestly I havent really lost much of my pregnancy weight. I’ve always been skinny, but when I’m pregnant I gain hella weight (went from 124 to 192 my last pregnancy) All of my clothes still don’t fit. Of course that is not my priority (hence the looking fat asf still 5 months postpartum) but I do want to start changing my eating habits now, and maybe start getting in track with my old weight again, BUT i want to breastfeed for at least 18 months + so I don’t want any of my calorie intake to affect my breastfed baby. My question is how much can I reduce my diet to? How many calories do I have to eat for sure? Im thinking about mostly eliminating carbs /butter and milk to start off. And drinking only water. (I started drinking coca cola when pregnant ew I used to NEVER before, and I ate whatever I wanted but I just didnt like soda) Any stories of dieting while breastfeeding long term would be really appreciated.