I wouldn't recommend anyone quit a guaranteed, full-time job right now. Millions have been laid off, many of those are now asking how to start a profitable stay-at-home business because they can't find a job.
You sound like you are underpaid or unhappy at your present job. Unless it is a job you know will end soon, or you are working in a hostile environment, I would hang in there. The competition for available jobs is brutal.
You seem to be starting off at step one, that is, finding something you can do freelance. If you don't already have the skill set or the clientele in your particular niche, you may find yourself in a severe economic pinch if you quit. I worry that you are asking strangers for suggestions on a good freelance business. It should be one that you are already familiar with, have good contacts in, and have a highly desired skill to sell. If you don't, please don't quit your job.
Further, if you quit, you are not entitled to any unemployment benefits. Quietly research good freelance opportunities that you know you can get clients for, start working in that area on your own time, part-time, until it looks like a winner. Then quit your job.