Think seriously about purchasing a hand-held GPS. The route is not well-marked and it is easy to get lost.
You can load in the maps from Wikiloc.
Smart phone. An alternative is a smart phone. There is good coverage on the Ignatian Camino and you can follow the route using Google maps. The only issue is that sometimes a smart phone will need to be recharged during the day. There are devices that allow you to do that.
A dedicated handheld GPS has satellite reception and does not rely on network coverage, has more powerful navigation features, and a better battery life than a smartphone with a map application. However, a smartphone app may be all you need.