Hmmm, that's a tough one. A boot that is too long should cause blisters on the soles of your feet, or the heel, as your foot slides around and lifts. Shouldn't cause blisters on ends of the toes. And a 12, from the same maker, isnt THAT much smaller.
The Escape GTX
So I'd pursue two tacks. One, there are makers out there that make a 12.5 boot. Scarpa does, for instance. Its Escape GTX ($220) is a good-fitting, extremely comfortable boot that's good on all sorts of terrain with a variety of loads, even heavy loads. I've worn these boots and like them a lot. You might also look at the La Sportiva Cascade GTX boots ($180). Not quite as heavy-duty as the Escapes, but a sturdy boot that should have the right size for you (both the Escape and Cascade are Euro-sized, but their 46.5 should match a 12.5 U.S.).
The other thing to do is find a good outdoor shop with a good boot-fitter. Ask around. There are lots of things you can do to improve the fit of a bootadd after-market insoles like Superfeet, stretch out the toes, add tongue pads to suck up volume, etc. There are all sorts of tricks. Get fitted late in the day, when your feet have swelled up a bit, and take your OWN socks to the store.
So if you take the time, and find someone who will be patient with you, I think you'll find a good fit.