Suggestions for new head unit

The Prius c is pretty easy to adapt to an aftermarket stereo- possibly easier than any of the other Prius models.

You can use nearly any double-DIN sized stereo. That is the most common industry standard size, essentially every electronics brand builds it. It will fit cleanly in the c dash. You will need mounting brackets and a fascia panel to complete the installation. Both are made by Metra and are often included with stereos bought from certain vendors, available separately if needed.

Many new stereos have oversize floating screens- some of these won't fit because they'll block the AC controls or vents. This is the latest new feature, and I haven't had a chance to play with many of these so I haven't spotted ones that do or don't fit the c. All of the "regular" ones without floating screens fit fine.

Think about how you'll want to use the new unit. You can get a new unit with GPS navigation built in, or you can get one that uses the GPS system from your Android phone, meaning no navigation at all unless you remember your phone. There isn't a way to retain the exact GPS system that came with your car.

You're going to need a translator box for steering wheel controls. This can be a big source of complication for DIY, or just another $100-150 at the pro installer, because they do them all day long. When done, you'd never know it was there, it just works.