Whats the upside of doing this?
What are the risks/downsides?
I’m not the smartest feller in the room, but I can’t imagine the answers to the first question being worth the answers to the second question.
No one here is qualified to give you a ‘no you don’t need a climbing rated harness’ answer.
Do yourself a favor- if you’re going to engage in risky behavior, do it fully informed. Don’t try to convince yourself because some random guy on the internet told you something was safe, that it is. There is a ton of information on this site. Read it, think about it, digest it, but don’t take the opinion of one person, or even a group of people, as fact. There are also loads of books and articles on climbing and safety equipment. There is likely a certified climbing instructor in your area. Don’t be lazy with your well being.