Spiti is a good option but you have to take shimla kaza tabo route as rohtang is closed in january. other than spiti you can go on trek like roopkund, kedarnath trek, har ki dun.
Hey Kshitiz, You can go to following places in Jan in HP : 1)Tirthan Valley 2)Parvati Valley ( Kheerganga and Sar Pass trek) 3)Mandi (Prashar Lake) 4)Macleodganj ( Triund Trek,Khajjiar) Hope this helps.