What small businesses are profitable?

What are some common businesses you’ve seen start up and do well? Meaning not be extremely rich but be able to pay bills and enjoy life sometimes.

I’m in HR but always wanted to start a business. Always been interested in staffing agencies but not sure how difficult it is and if it is even worth pursuing one day. What do you think? I’m already a gaining experience recruiting, screening resumes, interviewing, filing, laws, etc. and plan to work for another staffing agency one day if any openings.

But in the end I’ve always wanted to do my own thing doing something I’m interested in. Love dogs and even thought about a grooming shop and daycare but don’t think I can make enough to not worry about bills lol.

If you have any stories I would love to hear them.