If it's not iust the visuals, then that's a game-mechanics change.
For...ever..? the Industry Tree that the dwarves must follow is that even if nothing else[1] needs it, beds can only be made by wood (inc. subterranean fungal trees[2]) and is a gameplay dependency, much as is anything requiring an anvil[3].
Yes, in (e.g.) Minecraft you can merely karate-chop your very first tier-1 materials (from which you can evolve all later tier-capable production methods fairly quickly) in the initially unarmed, unburdoned and (aside from cosmetic skin) 'unclothed' Survival Mode character, but DF requires you to at least accept the default Embark (or New Adventurer) equipment , if not consider it (and the nature of your initial destinatiin state and hopes of what you find there) and adjust to best suit your gut feelings and/or sense of adventure and challenge.
And one element is if/how you're going to implement wooden beds. A rock bed seems no real advantage over sleeping on the floor, and it seems bedding (mattress, if not coverlets and the like) is not relevent whether sat upon a bedstead/sleeping-platforrm or growing as potentially more restful vegetation from out of muddy ground.
(In my head, I consider it perhaps a near-universal ploy to annoy the Elves. All other creatures have sweeter dreams knowing that they are reclining on cruelly cut-down tree-torsos, and that is enough to substantiate a nicer rest than just curling up in the middle of a corridor/battlefield/temporarily-empty-magma-sump. But that's just me.)
[1] Well, almost nothing else.. there's axles, etc
[2] For those who run out of/waste/lose/destroy/otherwise-lose-access to the inital wagon-dissassembly material, while on a treeless/trees-inaccessible embark and need to defer (more) beds until cavern-breaching happens. And for that you need an axe, which to forge anew you need an anvil[3], if you didn't (successfully) have one brought to the site...
[3] For which, to forge anew you need an anvil[3], if you didn't (successfully) have one brought to the site...
From a visual POV, there's already much weirdness (conversion of log to planked flooring, which can be ripped up to form an axle, a windmill blade, stairs of various configurations, wagon-tracks, a bit of bridge, and back and forth between however many forms you wish, before commiting to be carved or otherwise constructed into cages or cups, bucklers or beds, hatch-covers or hives, which do not tend to
look like they were bashed out of materials recycled from old constructiions. And there's no internal requirement to make
or fit door handles, hinges, brackets, etc, where quute clearly most graphic-packs would visually suggest that such a process has happened.
For that reason, until any major revamp of "industrial logic", let the bed (created as wooden 'for Reasons') be represented as a recognisable bed
despite the apparent (irreversible/unrecoverable and otherwise unexploitable) transmutation of a small amount of lignin to cotton, or whatever it might be assumed to be.
Well, that's my thoughts, such as they are. But they reign supreme
only in my own head (if that!), so I have no objection if anyone thinks differently.