However, I like to be able to write down notes and draw simple figures as if the device were a real notebook.
Yes, the iPhone has apps that allow you to do that.
However, I don't think you'll ever use a phone for that on any consistent basis, no matter which one you get. I thought I'd be writing hand notes a lot on my iPad too, so I bought one of those pens...and barely ever used it. It was so much more efficient to just type it, use dictation, or take a picture.
Need a reminder of something a few hours from now? Use Siri.
Need to copy down a drawing the boss made on the whiteboard during your meeting? Take a picture.
Making a grocery list? Use Siri, or open a task app like Clear and type it in.
Can't use Siri because it's a quiet environment? Typing is much faster than handwriting, and with the iPhone you can type with one hand while doing other things.
Do you really need the flexibility of a piece of paper for your detailed notes? Put the notes down on paper, then take a picture
Maybe if you gave a specific workflow you're thinking of, I'll chcange my recommendation, but it seems to me that drawing or taking hand written notes is simply less efficient, and will get old fast.