I've been an Ex-Officio fan for some 30 years. Back in the day, traveling internationally, I usually only wore and carried only three pair, no matter how long I was away. They hand wash fast and dry very fast. Rotating pairs was easy.
If you hand wash one pair each evening in your hotel, they are dry by the following morning. Ex Officio advertises traveling with only two pair - one worn and the other drying from the previous night's hand wash. But, I like to have the security of the third pair - just in case.
After retiring from my profession and finding the Camino nearly a decade ago, I quickly learned that the Ex-Officio boxer shorts continued to be the best solution for me when walking. I still use three-pair in rotation. That seems to be the ideal solution for me.
Keeping them out of a dryer after machine washing is very important to preserve the waist elastic. I hang mine on a wire hanger by the waistband to air dry after they spin dry. If you must put them in a dryer, use cold air only. Do not add heat.
If you are on Camino and have access to outdoor drying, they will usually air dry compactly in less than 45 minutes if wrung out well. In this case, I use clothespins / clothes pegs to fasten them to a line.
Merino wool is good - very good. But I cannot bring myself to wear wool underwear. T-shirts and various outerwear items made of Marino wool are fine. But, there is something off-putting about wearing ANY kind of wool - no matter how soft - next to my "tender bits."
Hope this helps.
Tom