If you are looking for a cheaper alternative to the Moleskine, the eccolo cool jazz journals are great, they have different sizes, ruled or graph, have a hard cover, pen holder, pocket in the back, and are cheap. This is the one I use, and it’s only $6,

Try using sand bags. Buy a couple cheap bags at your local hardware store and either hold them against your chest and squat, like a goblet squat, or put multiple sand bags in a duffle bag and put on your back.