Hi Eliza, welcome to the forum. My first thought is the Camino Primitivo, as you could walk from Oviedo to Santiago within your timeline. It's wonderfully rural, with lots of quality time spent hiking through hills and mountains. It's physically demanding, so you would need to be more fit for this than the Francés, but if you like hills I'm guessing you train well!
The one catch... you're hiking in March. That means the weather may be iffy. With fewer stops along the way, and more rugged terrain, you're more at the mercy of nature on the Primitivo. For that reason, you might still consider the Francés from León to Santiago. You'd have one good mountain crossing to O Cebreiro, and Galicia has nicely undulating terrain. After León, large urban areas are very limited. And, if rough weather hits, it'll be more manageable on this route.