Watercolor sketchbook post-mortem

A photo of my full-sized watercolor sketchbook. It's hand-bound with orange, yellow, and green thread. The cover is wrapped in lemon-print paper.
I only have a few pages left in my big watercolor sketchbook. This is an accomplishment for me because I usually have a hard time finishing sketchbooks, and I'm actually happy to look at this one despite not really using it for anything particularly fancy. It also means I have to think about making or buying a new one soon.
Liz Steel has a great post on this topic, How to Choose a Sketchbook. In the interest of thoroughness, I'll talk about the criteria she uses in her post.
Purpose
I had originally meant to put this book inside of my standard size Traveler's Notebook, but it doesn't fit in there very comfortably, and I learned that I don't enjoy that size for art on the go. (That job has since been relegated to my passport size notebook.) So the book ended up morphing into my stay-at-home sketchbook.
I've specifically been using the book to experiment with different media, techniques, and palettes. I treat it more as R&D than anything, which is a big factor in me actually using it. (You can see some older spreads and commentary on the previous sketchbook post.)
Paper
I almost exclusively use wet media. I prefer watercolor paper to mixed media paper because I need the paper to be able to take heavy layers of gouache without getting sad and crinkly. I also like cold press paper more than hot press, because of The TextureTM.
I make a point of not using beautiful 100% cotton paper because I'll feel like I have to "save" it for "real" art, which is counterproductive to what I'm trying to achieve here. The paper in this one is the cheaper Canson XL paper (300gsm), and I don't have anything bad to say about it (good thing, because I still have the rest of the pad to use up!).
Binding and cover
I bound this book myself using a single-sheet Coptic binding method. (I followed this tutorial by Sea Lemon.) It takes fucking forever, so I thought about buying a book to replace this one... but I don't think I can ever go back to fighting with a store-bought sketchbook. Coptic-bound books just lay flat, and that's become a non-negotiable for me. I haven't found a commercially-available sketchbook that behaves as nicely.
The binding job itself is pretty janky because this was my first go at it, but I've come to embrace it. It's... rustic? It adds character.
Format and size
I hate the size of this thing. The tall, skinny pages are really awkward to work with — I feel like I have to cram two sketches onto one page or be stuck with a weird amount of whitespace. I like the standard TN size for writing, but I can't stand it for art at all.
I'll be evening out the aspect ratio for the next book. It'll be roughly A5-sized because it's big enough to give me room to work with without being obnoxiously large. I'll also keep the portrait orientation because I find landscape books awkward as well. If I want to do a landscape sketch, I rotate the page or use both pages in the spread.

A photo of the inside of the sketchbook. The left page has swatches of Caran D'Ache Neocolor II crayons. The right page has two sketches of birds done in the same crayons. (Top: Grackle on a palm tree. Bottom: Egret on a pole.)
Number of pages
This sketchbook has 12 sheets in it for 24 pages in total, which was mainly because it needed to fit in the Traveler's Notebook cover. I might put a few more pages in there since that's not a consideration anymore, but I still want to keep the page count relatively low. I don't paint at home that frequently, so I'd like to finish the next book in a reasonable amount of time. (I think this one is almost a year old, which is a good timeframe.)
Conclusion
Everything about this sketchbook worked out surprisingly well besides the size. I've had a good time with this one despite the size issue, but I'm looking forward to having a fresh start (and bigger pages) in a new book.
If you don't feel like any commercially-available sketchbooks meet your needs and have the time and energy to invest in bookbinding, you should give it a shot! It's really freeing to have a sketchbook (or notebook) that meets your needs exactly.