You can try northern states.. shimla is good, temperature is perfect. other than that you can try shillong too. In fact shillong is very preferable at this time and you ll experience every weather in meghalaya. there you can go see the various rivers, go into dense forests, wild life sanctuary, Buddhist temples, etc.
It depends on from where are you traveling from. If it is from North India specifically Delhi then you are having good set of places for 3N4D. Jaisalmer Jodhpur Kheerganga trek Manala Kasaul Lansdowne Auli Parashar Lake Chopta Bir Billing and many more in the bits and pieces of Himachal Pradesh and Uttarakhand