La Paz-Sucre-Potosi-Uyuni - What to wear?

It'll be cold in Potosí and Uyuni. Jumper (and probably coat) weather by day, definitely coat and hat weather by night. La Paz will be a bit milder but still chilly (it's been getting down to 2ºC in the city centre this week, with snow in El Alto), Sucre a fair bit milder still.

depends what activities you plan on doing, but some thermal underwear, a good fleece and jacket would be wise. Also a good sleeping bag as you plan on doing the salar de uyuni. La Paz is cold right now but the worst is meant to be over with after this weekend and then the school winter hols break finishes. Potosi and Uyuni are always cold. Sucre has a nice climate and is usually sunny and dry.

Check out whilst in La Paz, the Loki Hostel calle loayza, Star of India curry house calle cochabamba, sol y luna and olivers travels calle murillo, traffic avenida arce and if you have the time, the WMDR bike ride. Gravity is the best option, B side is a good alternative.

Sucre should be fine, pretty warm. Uyuni and Potosi are both cold, espcially after sunset no one wants to get out of the room...

Bring a fleece and some longsleeves and your jacket. It gets cold in the Andes mountains due to altitude.
A sleepingbag would be nice if your doing the Salar de Uyuni tour.

Layers.

It will be cold at night. During the day it heats up a bit, but buildings remain cold. Everything you touch is cold. Your hands get cold. Your feet get cold.

You would be very wise to choose hotel rooms that have large windows facing north. This will make a 15 to 20 degree difference in temperature inside your room, especially in the evening.

Peter

Thank you all for the useful advice.