Help finding hashtags

So my account is at 5.7k and I'm kinda sick of the follow/unfollow method so I've been trying to find a way to grow organically (with a boost). I've bought a SMS to give me 1,500 likes on up to 4 photos I post everyday automatically to help me get into top posts. But I think the hashtags I target currently are a little too big and competitive because I'm still not making top posts in any of them.

So my question is, what's the best way to research and find the most relevant hashtags for my niche, that are small enough that I can make top post in?