Straw stuffing is really more period appropriate, don't you think?
And any system to obtain straw would be so trivial as to merely increase the amount of (lag inducing) hauling going on.
I agree. I think a lot of us are thinking in modern times where we have inner-spring mattresses with space age stuffing. In the time period DF is set in, most commoners slept on straw pallets. Only nobles had feather beds, it was very hard to find enough feathers to stuff an entire mattress as they were used for other things like fletching. Straw, on the other hand, was dirt cheap, and fairly soft.
I could see mattresses being stuffed with straw (which would be done by default for abstraction), feathers (which would be gathered into bags at a butcher's shop from chickens or wild birds), sand (which would make them absurdly heavy), or cloth.
Essentially what I'm thinking of for revamping beds is three types of bed - bedding, mattress, and bed frame. Any one of the three can be used for sleeping, and any one of the three will reduce unhappy thoughts. One of the three will halve the unhappy thought from sleeping on the ground, and if placed in their room will reduce it by 75%. Any two bed items would remove the unhappy thought and if placed in their room will allow them to "admire" their own bed. All three would result in the "Slept in a warm bed" happy thought. At any stage, the quality and material value of the bedding would effect the value of the thoughts associated with the bed.
In order to place the beds, a new menu would have to be added where the current bed menu is. 'b'->'b' would take you into the bedding menu, which would have options for bedding, mattress, bed frame, frame with bedding, frame with mattress, mattress with bedding, or complete bed. From there it would be built like any other object that requires multiple items, and when removed it would break down into it's component parts.
While this might be difficult for new players to pick up, when/if a tutorial is created it would be fairly easy to instruct new players to build some bedding, then later tell them about creating mattresses and bed frames to make their dwarves even happier. As is, the only real detriments to dwarf happiness are hated vermin, death, and destruction of artifacts. All the other unhappy thoughts can be controlled with a legendary dining room and maybe a waterfall.