Just to let you know - BMI healthy weight range is 20-25... 19 is actually underweight. It might be difficult to maintain this weight because your body usually responds to being underweight by slowing its metabolism and holding onto food.
Can I recommend the lowest you go is BMI 20? BMI is not highly accurate, however, it tends to overestimate rather than underestimate. That is, if your BMI is 28 but you are very muscly, you are probably within the healthy weight range. So a BMI of 20 is a good aim if you want to be skinny, or if you want to have more muscle mass, aim for BMI towards 25.