As I've said before, I'm most comfortable and even more creative when I write with a pen on a pad. My
favorite size is approximately 5x8, as it fits in my smallest Coach purse.
I journal daily, but this time of year I carry a second notebook that is dedicated to my NaNo Novel. I did the math and @ approximately 7 words a line, 25 lines and 80 pages front and back, I can get 28000 words in one notebook, which is a little more than half the objective wordcount for NaNo. I'll blow through 2 notebooks
They're available at the big supply stores. And although I prefer the classy Mead Cambridge below, Walmart has some smaller cheaper brightly covered ones that I use for my daily ToDo List that stays on my desk and other small projects.
If you're an internet shopper, you can order from Amazon.