I am climbing Kilimanjaro in January. my feet tend to get cold very easily and I needed to wear plastic mountaineering boots on Mt Ranier when I climbed it in the summer. I know Kilimanjaro is near the equater, but I assume teperatures will be cold at 19,000 feet none-the-less. Any single boot recommendations for both the climb and the trek in to the base?

This boot is perfect for the climb and trek. Make sure you break it in by wearing it before heading over to Kili. Have fun! I have climbed Kili a few times by a few different routes and it is always fun. You will most likely have porters, so bringing a pair of light runners is not a problem. If there is no snow on the trail, a pair of light runners with gaitors and toe warmers. I use the toe warmers on top of my toes and poke small holes in them with a pin or pointy knife at altitude. This allows more oxygen to get to them. Beware: the toe warmers burn hotter and last LESS time when allowing more oxygen into them, so bring extras. They are worth their weight in gold to me and have saved me from frostbite on numerous occasions. May this help and may you have a safe, fun and successful adventure!

I don't think you want to or need to carry 2 different boots. You definitely don't need plastic boots for Kili unless you are doing a specific technical route (which not many people do there especially now that the glaciers have receded). Anyway, if you are doing one of the main routes and as you say your feet get cold, I think you could get away with a thicker sock and a leather hiking boot (more comfortable and easier to break in and deal with than a plastic boot). I think the temps probably won't be any colder than the single digits at 19000 ft and as the sun comes up it usually warms up pretty nicely, unless it is windy.