I use good ol' pen and paper to get a (very) rough idea on paper, then switch to Canva, where I can easily drag things around, resize them, etc. It has excellent positioning features to line things up and evenly space things out. For organizing reference photos + thoughts, I use Upnote, which is a fine (and far more affordable) riff off of Evernote. I can add images to a note, so I upload a screenshot or download an image of other people's journal pages that I like and then list my ideas for how I would change/improve them.