Hi, some of the popular hill stations in the north are Bir-Billing, Kasol, Dharamkot and Khajjiar. Solo-traveller meccas are McLodganj, Kasol and Manali. If you want to go to slightly off-the-beaten-path hill stations then the options are Kausani, Naukuchiatal, Gushaini and Parwanoo. You can also refer to the attached article for more options in the north.
If you can head a lil east along with the northern hemisphere - Meghalaya, chirapunjee , Gangtok , Shillong , Sikkim .. these are bloody good places and a heaven to solo travellers . People there are super friendly!! And the views woooooah!!! Are mind boggling