Turtl would be great if not for the reliance on a server. I think they do some caching (their settings page has "erase local data") but since it relies on a login anyway it still requires an "always on" connection.
I agree completely on Laverna, but I think it's the closest to what you (and I) are looking for. I wish I wasn't so lazy/busy and got the motivation to fork it and implement the changes I want (I don't care for the double panel and the white space everywhere).