You may want to consider using Ipe'. This is a very dense wood, readily available, that is used for flooring on steel hauling trucks. It has recently become popular in my area for deck floors on houses. It looks like very dark teak and has an oily feel like teak. It is almost impossible to burn.
I am a cabinetmaker and almost any wood you use will deteriorate and/or discolor when exposed to sun and weather if not carefully cared for. We have milled bed boards for some of the locals in our area of various species, even walnut, and they seem to be happy with the result. So, I would go with what you like and take care of it.
Properly cared for your bed should last a long time.
