My goal is to make hardwood slats for a 4' wide bed, (center support, so span is 24"), thin enough so my heavier parts flex, adding comfort so I can minimize mattress. (Ideally, pad will be 1 inch cork, a nylon 'Persian-style' rug, and a very thin bed futon. I am thinking Japanese style bedding, minimal cushion. It needs to be thin to flex under my weight, but not so thin that ot causes degradation that excessively shorten it's life-expectancy.
I saw the swing discussion, and thought about the International Council of Building Officials books, and tables that I used 40 years ago to determine thickness of joists and rafters for given spans, dead or live loads, pitch, etc.
I found a series of tables for hard and soft woods in a PDF download, I don't have the link, but it is titled, "Chapter 4, "Mechanical Properties of Wood," by David W. Green, Jerrold E. Winandy, and David E. Kretschmann."
I am struggling to grasp the understanding of the data. If someone would like a look, I think I can attach it to an email & send it.
Back to my problem: I am thinking of going with 3" wide ash stock, ripped to 1/2" to 5/8", to span the 24". I would like the board to flex at my shoulders for instance, to cause the bed at my shoulders to support an equal amount of weight as my abdominals for instance.