Just like the title suggests! Toady already talked about coding new multi-material instruments (he mentioned various textile strings on a wood/metal frame). For years we've been talking about making beds out of other materials. Some have even mentioned carving them out of the stone when mining out rooms! However, I've always favored frame+padding+fabric/leather. Since we will be able to generate wood instruments with jute strings, why not a stone bed with feather padding covered in silk?
Not only would this give a purpose to some rather useless objects in game, but it just makes more bloody since and prevents the whole "no wood, no beds" issue. We can use stone/metal beds and then make mattresses out of the chicken feathers, (unprocessed) wool, and animal-hair as stuffing. Currently, you tend to produce far more animal-hair thread than your hospital can use... especially considering your sneaky doctors tend to grab your masterfully dyed GCS thread for suturing... bastards. Straw and various leaves (palm fronds namely) have historically been used as beds too. On that note, straw could be a useful by-product of harvesting/processing grains. Not only could it be used as mattress stuffing, but could be burnt as a fuel or woven into hats, but that is an entirely different topic!
Hell, the ancient Persians even had water beds XD.
Early on, we can just make simple beds that are little more than a slab/wooden block as we have them now. We can also make cots that exist as frame+sheet really (leather or unit of cloth). Then there would be the deluxe bed as we know them now... frame+mattress+sheets. This could even be a noble requirement! Other than decorations, do you really think your good-fer-nothing noble wants to sleep on the same bed as MERE PEASANTS!? No! He wants a candy-frame (pimped with diamonds), roc-feather filled bed covered in GCS silk dyed as black as the lump of coal he has for a heart.
Frames would be made by whoever the hell handles the material. Carpenters would naturally make wooden beds and blacksmiths metal ones. I suppose potters could make clay frames? We can then place that bed as we normally do for basic sleeping. Later, we can go to a clothesmakers shop/leatherworks (or just a craftdorfs shop) to make the mattress. We'd select "cloth/leather mattress" and then select the bedding material as a sub menu. I imagine using a similar setup to making gem windows for placing the full bed. First we'd select a frame then select a mattress. Mattresses could also be thrown on the ground to count as "cloth" beds, but only mattress+frame would count as a "full" bed. To differentiate between the two, we could rename the bare frame to just "cot" and save "bed" for the mattress+cot.
For practical purposes, better beds would not only increase happiness but let dorfs rest better. They could get a "well-rested" buff that gives them a buff to their energy (fatigue slower). Sleeping in the dirt could also give a penalty- this would also incentive building early beds. As it stands, they only grumble a bit until they see a couple of statues or a "well built" bridge. The main point of this is to alleviate the "wood crunch" on low-wood maps. Sure, we can breach the caverns... but giant cave crocs and trolls live there too. Generally, we'll need wood to build traps before breaching the caverns to gain the wood for said traps (plus beds). Wood is often needed as a fuel source for metal smithing as well (for metal cages/weapons). The other points would be added realism as mattress date as far back as the neolithic (that we know of) and virtually ever civilization has their own version of them. From throwing padding on the floor to straw mats to hammocks to elaborate canopy beds (speaking of hammocks, rope+couple of clothe units would count as a bed). The final reason is trying to find a bloody use for animal hair and feathers >.> I just hate accumulating so much useless stuff. Its especially glaring with feathers. Its not like any civilization has ever tried to decorate clothes, weapons, and/or furniture with THOSE. *sigh*