A kilo on your feet equals six on your back in terms of exertion needed to move you forward. That’s a lot.
Spain is a modern and very well developed country. This isn’t a walk in the Andes or Sahel, it’s a stroll through something one could rightfully call “Spanish Suburbia.” Most roads are well fortified, some existed since the Romans used them to move their goods and soldiers along the North of the country.
You really don’t need hiking boots. The much mentioned “ankle support” offered by such shoes is quickly offset by the additional strain on your ligaments and resulting loss of finesse and stability.
After a boots disaster on my first Camino, I exclusively walk in Trail Runners. Those shoes are built to be light and yet have a great profile for the few times you need it. They’re however also usually certified for 1500 kilometers, meaning you’ll need a new pair for every Camino. Which isn’t too bad, the $90-120 you pay for them are a real investment in a better Camino experience.
Some brands (no endorsements)
In my experience, stay away from “culture shoes” like Adidas or Nike - they’re generally much more expensive and less geared towards what you’ll be using them for.
Upgrading on the Go
Most larger cities (Pamplona, Burgos, Leon, etc.) and many smaller towns and cities have shoe stores or dedicated hiking/pilgrim ones. After Pamplona you’ll find the next one in Logroño, for example. If your shoes die and are usable, walk there, otherwise just call a cab back and forth and you’ll be all set in hours. If you’re worried about blisters in new shoes, don’t be. Get good socks and you’ll be all fine. See below.