I was a single founder when I started in 1994. Since then, I have had several businesses - none of them have been $10m businesses, but they have brought in great income. I grew two of them and then installed managers to take them forward - I still own them. Some thoughts from me:
1) I tried co-founders, but found that they didn't work as hard as me. Most people like to be lazy, so finding someone with the same work-ethic is difficult
2) I want to make decisions quickly and having a co-founder could slow that down for me
3) Employ people quickly who can help you. You don't need to give up part of your business to get good people. What motivates people is not just money - its often pride in a good job, good working conditions etc. I always run a very flexible in terms of time that people work. They work when they want and always get the job done
4) Don't be afraid to fire people. There are "givers" and "takers". I always fire takers as soon as I recognize them.