The truth is collaboration is THE way to grow your channel. Nothing else comes close. Unfortunately, big YouTubers rarely collaborate with small YouTubers. Fortunately, YouTubers who have around the same number of subscribers as you do are the ones most likely to be willing to collaborate with you. So search for YouTubers who are doing what you're doing, subscribe to all their channels, be an active viewer (leave comments on EVERY video of their you watch), and then come up with a great FUN idea for a collaboration and pitch it to those who have around as many subscribers as you do. Pitch it also to your niche's big YouTubers but don't hold your breath that they'll bite. They might and that will be GREAT! Just don't expect them to UNTIL you're as big as they are.
And don't stop with the above. Fish in other ponds. In fact, given your channel's shtick, you should have an easy time pitching collaborations to other YouTubers in other niches. Have them teach you their skill!
Always ... ALWAYS make two-part collaborations. Part One goes on the bigger of the two channels and, at its end, links to Part Two. Beginning of Part Two links to and encourages the viewing of Part One.