Why? Are you seriously going to risk your health so you can see your rib cage "just because??"
I was 120lbs at 5'8" for a while, and I look like a ghoul in every photo from that era.
I promise you, once you can see your rib cage, you will realize that you don't actually care about being able to see your rib cage.
You're talking about a major decision which will lead to a minor outcome that you will forget about after a week.
You are talking about damaging your brain for a body aesthetic you will grow out of a month later.
For the love of God; find something else to make you happy. Anything other than letting your body waste away.
I say all of this out of love. I don't know you, but I want you to be okay.