Your Degres ($295; www.koflachusa.com) should be more than adequate, Brian. Sure, it can get plenty cold in the Bolivian mountainsdown to minus 15 Fahrenheit at nightbut the Degre is designed for cold weather. I don’t think you’ll need the Alveolite liners, nor a full overboot, as you would for Denali or Everest or some other super-cold, high peak.
Meanwhile, there are several things you can do to make your Degre boots warmer. One, replace the insole with an insulated insole, such as the Insolator ($8), a layered insole with neoprene and Thermolite that blocks cold coming up through the bottom of the boot. Two, take good, warm wool socks, which I’m sure you’ve worn on Hood and in New Hampshire. SmartWool’s Mountaineer ($20; www.smartwool.com) is an excellent cold-weather sock. Third, pack some vapor barrier socks. These are simple nylon socks, usually about $25, that you slip over your regular socks before putting the boot on. They add 10 to 15 degrees of warmth by eliminating evaporative cooling, which is what happens when the sweat on your feet dries. They work very well, although the downside is that they make your socks damp, so carry plenty of spares.
No doubt you’re researching the trip carefully. Two problems worth anticipating are the need to acclimate very carefully, so you don’t get a good dose of mountain sickness, and the difficulty in finding decent, clean fuel. Take an MSR XGK expedition stove (www.msrcorp.com), and carry plenty of spare nozzles for kerosene, gasoline, and other fuels.