Ordinary Sausage makes sausages out of… unconventional ingredients and is hilarious at it.
I likewise love Steve’s channel. It’s been about six months since his last upload, I hope he hasn’t run out of MREs!
Another passionate, positive creator that I enjoy is Grady at Practical Engineering. He brings a real joy to demonstrating nerdy civil engineering challenges via plexiglass mockups in his garage.
Angie from Transcend Furniture Gallery is just so nice and sweet. She loves what she does and it shows.
Todd of Project Farm is always remarkably excited to conduct (what must be for him) exceedingly tedious (and thorough) tests on workshop tools, chemicals, hardware, etc.
I’m surprised he hasn’t tested hearing aids. 
I don’t know what counts as niche, but LockPicking Lawyer has over 4 million subs, so I assume if i stay under that, I’m fine.
I’d recommend Hermitcraft, especially GoodTimesWithScar. Its just a bunch of people, mostly in their late 30s and 40s, playing Minecraft together. Its nit exactly for adults, but not really for kids, either. It’s not frenetic or, well, stupid, like most Minecraft Youtube. It’s just people who really like to place blocks playing survival Minecraft together. There are storylines and pranks, but it’s mostly building and farming.
And the stuff they do is amazing. So creative, so clever.
GoodtimeswithScar is my favorite. He’s severely disabled but still just has this powerful attitude and managed to find this way to express himself (and support himself) when his disabilities pretty much ruled out all the traditional ways he could have shaped his life. And his eye for color and shape and texture blows me away.