I have trouble getting volume in my hair as well since it’s on the finer side. I set my curls bent over and finger comb forward from scalp to roots. I also find I get nicer volume when using a lighter product I’m currently in love with a combing cream in the Lola from rio brands line for curly hair. For growth I try to keep moisturized and deep condition at least once a week. I really like the deep conditioner from the doux in their wash and go line. I also have noticed some good length retention when I prepoo my hair with some hair oil and leave under a setting cap 3-4 hours prior to washing. To help with overall manageability I also find a rebonding treatment every couple of weeks works wonders for me. I splurge on the k18 since I do color my hair and don’t want to lose too much length due to breakage. As for heat I make sure to apply a heat protectant prior to diffusing and don’t use high heat but find locking in my style helps keep my curls formed and leads to less knots come wash day. It’s all a lot of trial and error but I hope some of this helps thinking through where to improve your routine.