I have been stupidly struggling to make my own moleskine-like book for the last couple months. I use a single signature (14 pages of regular copy-weight) with a paper covered cardstock cover and either sew it from top to bottom or phamplet stich it. Then I glue a strip of paper backed book cloth to the spine and press. What always happens is that the book will NOT lie closed 100% flat. Because the structure is so simple I cannot figure out why this is happening.
I fold with the grain of the paper, I crease tightly, I try to make sure that my thread is thin enough, then I bang my head against the wall in irritation.