Do not forget to include the all-important for the Camino qualifier... Is it right-sized?
Many shoe style run slightly larger or smaller than the advertised and marked size. Do advance due diligence to determine if your 'target' shoe or boot is true to size. Make size estimate adjustments, up or down, from that point. For example, several Keen styles run 1/2 size larger OR smaller. I have had to adjust accordingly. Start by checking with the manufacturer or distributor. Then check with shop staff. Finally, try them on with the socks you plan to walk in.
Also, and there is still a debate on this point, size UP to accommodate a second pair of socks, end-of-day swelling, and possibly splaying after several weeks of carrying a daily load. I personally advise adding on-half size for each of these considerations.
So, in my case, my Keen Targhee II boots, running 1/2 size SMALLER than posted, needed to be a full TWO SIZES larger than i measured at the time. That was an extra:
1/2 size for the smaller than posted style issue (per the Keen website)
1/2 size for the second pair of socks
1/2 size for the end of day swelling, and
1/2 size for multi-week splaying...
Bottom line, my Bannock-device measured US size 11 / 44.5 feet needed a size 13 / 47 Keen Targhee II boot. Your experience may vary. For me, this worked perfectly. In six Caminos, I have never had a blister... not bragging, just a fact. I have other foot problems, but blisters and lost nails are not among them.
My bottom line here is that the boots ought to be on sale if that is important to you. But they must be comfortable, and fit according to the Camino standard.
If you buy the same size as you wear on the street, you will have toe problems. Toe blisters and lost toenails are frequently caused by the toes striking the inside of the toe box on downhill stretches. In every case where I have attended pilgrims with this issue, they have shoes that are the same as street size, or maybe 1/2 size larger. Too small footwear is always a proximate cause of toe problems on Camino.
Hope this helps.