While several here have already extolled the virtues of Zenith brushes, especially the wonderful B2, I’ll throw in a quick plug for Whipped Dog’s boar knot. I just recently picked up a 30mm WD boar knot and have been quite impressed by how easy and soft it’s been while breaking it in. It’s been just a few hand lathers, and I think it might be ready for prime time soon. Good luck in your search.