Thanks for the insight.
Just to be clear on footwear--
Are you saying your "three pairs of shoes" are:
-an everyday walker
-sandals
-flip flops
?
Did you wear socks with your sandals?
That's right.
I originally started with a pair of Columbia waterproof hiking shoes that were fairly well broken in. However, I didn’t anticipate how much my feet would swell, and the intense heat caused me to sweat so much, my socks were constantly damp, which led to some awfully painful blisters. I suspect the waterproof feature of the shoes limited breathability, making things worse.
In a desperate attempt to alleviate the pain and keep going, I decided to buy a pair of Teva sandals and also a pair of Altra trainers (which I love because of their wider toe box), and I shipped my original shoes back home. It was a bit of a gamble since I wasn’t sure if they'd work, but fortunately, they did. That's why I kept the trainers, the sandals and the flip flops with me for the rest of the way.
I’m not certain which one resolved the blister issue, but I managed to stay blister free for the rest of the Camino. The Columbia shoes are still great and comfortable—I’ve even used them for shorter hikes since then—but they just weren’t the right choice for a summer Camino.
To protect my feet from gravel and add some extra padding, I wore the sandals with socks, occasionally even double socks on cooler days. Once the blisters healed, I sometimes wore them without socks at all.