If you are really concerned about raising prices (I wouldn't be; I think you should raise them across the board), you could try just charging new clients/users the higher rate. Adds complexity to your system, however.
Edit - just saw the question. The problem right now is not that you don't have a partner; it's that you don't charge enough for the work you're doing. Adding a partner is going to create another set of distractions and issues.
Edit - just saw the question. The problem right now is not that you don't have a partner; it's that you don't charge enough for the work you're doing. Adding a partner is going to create another set of distractions and issues.