Can you plan using a mindmap? I think you need something more visual. I would work out what you need to include (outcomes, tasks, assessment etc) make each one a new ‘arm’ and include what you need for that aspect in the cloud. I’m an ECE/primary teacher so not much help with high school.
https://www.ayoa.com/imindmap/blog/mind-map-your-lesson-plan/
I found this link which kind of explains what I’m thinking. Hope it helps!
Best may depend on your needs. Ayoa , for instance, has lots of features including visual task management, fast brainstorming mode and a handy zoom feature. You may not need all that.
Other mind maps may only have basic features. The way you interact with them may also differ. Some may make it easier to create and manipulate nodes. A lot of them have free trials so you might try some out. I don't know anything about iOS availability.
Look at https://www.ayoa.com/previously-imindmap/
IMindMap is now "Ayoa" which is an online collaborative "experience." One new feature that I like is brainstorming mode where you input ideas fast and drag them into the map as needed.
Lots of mind maps support images, photos and attachments.
I do more concept mapping than mind mapping sometimes. Some Mind Maps like Xmind support Concept Mapping but I think programs like VUE work better at that since VUE by Tufts University is a dedicated Concept Mapping program. VUE supports layers similar to what you'd find in an image-editing program. But VUE doesn't have collaborative support or the ability to attach media in the way you might like. That means
I work with several programs to ensure that I get the benefits of them all. You can also look at TheBrain which technically isn't a traditional mind map. You'll have to read up on that to see why it's not a traditional mind map. It's not cheap. And then there's SimpleMind.
Since Mind Maps are basically outlines in graphical form, you could also, as needed, use outliner like WorkFlowy or Dynalist. We can see this duality by viewing a mind map in outline form or exporting nodes from a mind map to an outline or importing an outline into a mind map program that supports importing. Sometimes I type up an outline in a program like Notepad and import it all into a mind map program which displays it as a mind map.