So of course, I made a case for it! I had a look at a lot of other tutorials, but none of them were exactly what I wanted, so I designed my own. It's closest to this tutorial, which I used for some construction help.
I used my newly delivered Walk in the Woods fabric, which I am still so in love with!
I still need to add some velcro as a closure, but I love the result so far! Now my DS can travel in safety and style!