moleskine: always reliable. they have a6, hardcover, elastic band, all page styles. a little pricey but ive never regretted.
travelers company notebook: pricy but absolutely worth the investment. you can refill it, and have up to 3 booklets. i usually have a blank, a “sketch paper” and either watercolor or blank ivory. they have lined, graph, calendar, etc as well.
its not hard cover, but it has an elastic band
kokuyo campus notebooks: not really “art” notebooks, but my all time favorite for notes. they have lined, blank, grid, etc. also not hard cover
ngl i also just go on amazon a lot for journals