So in this question, suppose I wanted to call a bed scarf/valance as a/an 'X drapery', where X is the word I'm looking for, which should mean 'of or pertaining to a bed' (or any place which is lied upon to rest, really). Is there such a word?
English commonly forms closed compounds in which bed is the attributive noun: bedsheet, bedstead, bedlinens, bedclothes, bedskirt, bedspread, even bedbug. German follows a similar pattern: Betttuch/Bettlacken, ’bedsheet’, Bettzeug, ‘bedlinens’, or Bettwanze, ‘bedbug’.
While neither of these two Germanic languages has felt the slightest need to form an adjective from bed, there was one readily available in (new) Latin: the scientific name for a bedbug, Cimex lectularius, the second term formed from lectula, dim. of lectus, ‘bed’. You can see this etymology behind French lit or Italian letto, ‘bed’.
This could have yielded *lectular in English, had anyone bothered to coin the word. In the late 18th c. there was yet another attempt to enrich medical jargon with a Latin-derived term, lectual, to mean ‘bed-ridden/bedfast’, but it‘s easy to see why that particular coinage never got off the ground: far too many English words derived from lectus, the past participle of legere, ‘to read’ (lecture, lection, lectern, etc.), and while reading in bed may be pleasurable, trying to form an adjective from lectula or lectus ‘bed’ is etymologically confusing.
So, no, there is no adjective form of bed in English, and the usual sources of new coinages — Greek, as you've seen in another answer here, or Latin, either directly or through French — were not conducive to fashioning a new word for which no one has felt any particular need — at least until now.
A simple answer is "bedding".
As in "We sell bedding".
Or in your example, something like "a bedding drapery".
Or something like "We sell every bedding article, from pillows to poufs to drapery and even mosquito nets and sleeping bags."
Note too that simply
does make perfect, absolute, sense and sounds natural.
(This is no more unusual than saying "car parts" or "dog biscuits".)
(It's totally commonplace in English that you can use, basically, any part of speech as another - you can turn pretty much any word in to a verb or adjective or adverb. In this case it is totally natural-sounding. You are mistaken to think it's not a "real" adjective - just saw your comments above!)
There is actually a common adjective which ultimately derives from "pertaining to a bed", but I think it will surprise you, and ultimately not be useful for your context:
1620s, "bedridden person, one confined to his bed by sickness," from French clinique (17c.), from Latin clinicus "physician that visits patients in their beds," from Greek klinike (techne) "(practice) at the sickbed," from klinikos "of the bed," from kline "bed, couch, that on which one lies," from suffixed form of PIE root *klei- "to lean."
To find a more suitable term, you might look for more words ultimately derived from Greek kline (like, for example, incline).