Hi, recently went to Nepal last december, the temperature there should be around 10 degrees-ish, you would only need a down jacket if you are going to trek to everest base camp. Highly recommend bringing some water purification tablets (can be bought in Guardian) as the tap water is not very safe, even after being boiled. Also prep yourself for consistent (but short) power outages, so always have a torch on hand. Have a safe trip!