I would recommend not advertising at this stage since you are doing well at the moment but I'd say work on SEO, high quality content etc.
One thing that I noticed when I looked at your keywords for a few videos is that your keywords as hashtags and that's hampering search ability as people don't search as much by hashtags in my opinion.
I think this video from TubeBuddy will help you reaching the new viewers.
View: https://www.youtube.com/watch?v=lkxpTrhatL4