Your ceilings are low. Choose a simple fan, 3 arms without lights. If you MUST have a light find something unobtrusive kind of like this

Because of the ceiling height, Id find a fan that blends in with it colorwise.. 42” is my guess

52 would be fine.

We put a 60" in our bedroom last year which is about 17' X 18'. It's closer to square than your room. My husband the retired engineer says he prefers to get a larger fan because then you can move more air at a lower speed than with a smaller fan. I can tell you that size doesn't look big to me. I was surprised when he told me it is 60". Look for ones with DC motors as they operate more quietly which is important in a bedroom.