Hello , I would suggest Haridwar and Rishikesh , they are religious and spiritual place where you will feel relaxed and peace. There are more nearby place where you can visit. Other then that Choptta is also the best place . The surroundings and atmosphere is too good.
Rishikesh is a very good option for solo travellers. You can find cheap hostels and seek peace at yoga ashrams. various adventure activities can also be done.