I have had the cat notebook cover shown below for four years and it has held up so well. The little cat on the cover looks so much like Ziggy. It comes from Lorenzo Dini Firenze.
It has 4 elastics and I use plain notebooks in it. Recently I bought two plastic folders and two notebooks (the one with the plain cover has unlined Tomoe River paper, and the one with the design on it has faintly lined paper) for it from TheChelseaPaperCo. They fit perfectly and the quality was great. I have found that plastic folders – whether for ring organisers or traveler’s notebooks – are often flimsy and tear easily. These ones are nice and thick and so well designed. I recommend this shop – prices are good and shipping from the UK was really really fast. When I bought, international shipping over a certain amount was free.