Feel free to adjust condensed milk quantity to taste. You can use sugar and additional milk to replace condensed milk. In that case, cooking time will increase to achieve the desired stickiness.
Add nuts, raisins if you like. I usually keep the traditional version without any additional ingredients.
At my family, we always preferred the soft naru/laddu. However, there’s another version where the coconut is cooked until the sugar crystallizes making the naru hard as it cools. Additional sugar is needed for the harder naru.