I just do.how do u solo bosses?
I play the game so much with everyone in my house that I'm always at a high level.
I would say play online and do some grinding. Raise the difficulty so that you gain more experience and better items.
I don't have any problems beating the game by myself. You can change the difficulty to meet your level if you're having to much of a hard time.
If I remember correctly I'm playing on torment 5 or 6. I need to bump it up because with my wizard I can dominate most situations. I want to work my way up to the max difficulty.
Is there a particular boss you're having trouble with?