Hello,
Just do what you do so far. Your doing it alright. Next, doing shouts and put some money into adds is always the best solution. F/UF is good if you want fast growth but not quality. Giveaways are best and fastest but don’t be discourage if you grow slowly. If you post good content and it’s yours, sooner or later you will start to grow big and fast. Do a story shares of other people who are in same niche as you. You will appear into someone explore page once they like a few of your posts. Also, be active with new followers, try to respond to comments as soon as they post them, engage with others a few times a day. Keep them engaged with your posts. You can buy followers but that will definitely destroy your account. (i wouldn’t recommend it to anyone) There is no shortcut. Your account is aged also so that means you can do a lot of follows and unfollows and likes without been blocked. But don’t push it. Also, check this post (Instagram Growth Strategy 2019)