>>513942Well stretching can add width but it can't add length.
Honestly I'd measure your feet first to make sure you're chasing the right problem. Brannocks are actually really easy to use. They measure three things, heel to toe, heel to arch and width. The first is easy, it's just how long your foot is. The second is the little curved slider on the side, that measures the proportion of your arch (slide it up till it's cupping the ball of your foot. On any given day, my to-toe measurement is about an 11, but my arch is closer to a 12 so I think of myself as a 12 with stubby toes. Most of the time I can split the difference and go with an 11.5 but sometimes I need an 11.5 wide or a 12, depending on the boot.
The flatvslider is width, just snug it up against the side of your foot. In men's typically A/B is narrow, C/D is medium and E-EEEE is wide. Basque "Wide" is about an E, whereas Merrell is usually about 2-3 E so not all wide sizes are the same.
If you really are a 12.5 wide, you're not going to find much from US makers that will fit you, try some European brands. They build their boots on the EU sizing and usually round up when calculating to US sizes. The Lowa Renegade is an all leather boot that comes in a generous 12 as well as 2EE wide.