My favourite small festival is supernormal by a mile. But may not be for the OP as it is mainly tuneless pan drumming that lots of us on here pretend to like (I love it).
Other small ones I’d recommend:
Red rooster in Suffolk (if, like me, you like punk rock blues. Last year was king Khan and bob log iii)
Cloudspotting in lancs. I haven’t been for a couple of years but is in a lovely location and usually has some good music involved (last couple of years have had for e.g. Ezra furman, lovely eggs, wave pics, haiku salut, kiran Leonard, king creosote. That type of thing).
Indie tracks is good but it largely depends on your indie pop threshold. I thought mine was quite high, but after a weekend at indie tracks it would seem it is not high enough. I’ve only been once.