First of all , All the very best for your solo trip. I can bet it will be your one of the best trip of your life. Myself being a solo traveller can say when you start enjoying your own company then there is no looking back.
So big cheers for that 💕
Coming Back to your questions. Listing down some places which can be covered in a single trip. I can assure you these trips will change your perspective about life , about yourself.
1) Shimla >> Chail >> Kufri >> Naldera >> Tattapanni 2) Narkanda >> Yalu Kanda (World's height Krishna Temple) >>Hatu Trek 3) Spiti >> Kaza
4) Manali >> Solang >> Sissu >> Atal Tunnel >> Kullu 5) Jibhi >> Tandi >> Bijli Mahadev If you want to go little offbeat and want to do some trek which results in a very powerful positive feeling at the end , then I would suggest you from my personal experience go for PUNCH KEDAR Trek.
These Include - 1) Kedarnath Trek 2) Rudranath Trek 3) Madhyamaheshwar trek 4) Tungnath Trek 5) Kalpeshwar Trek Note : You can go for 1 trek at a time.