I'd run shelves to fill the space. I'd find some nice wood at a lumber store --- they will usually cut to size. That said, Home Depot has a bunch of shelves. You can paint or stain them. I wouldn't worry much about how you attach them --- if they are full of books, no one will see the hardware.

I would recommend measuring very carefully. My husband measured a closet once and discovered, after cutting all the shelves, that the width of the space was different at the top and the bottom and the front and the back. Each spot a shelf was going to go had to be measured separately.

these come in white and black.

Easy.

https://www.amazon.com/WEKIS-Floating-Invisible-Brackets-Industrial/dp/B0C537PFLZ/ref=asc_df_B0C537PFLZ?hvdev=c&hvcampaign=626756832833&hvadgroupid=2680087945710&hvprdptid=4260609510989&hvprdgrpid=4672993505001&hvcr=4260609510989&hvadid=4260609510989&hvprdid=b0c537pflz&tag=ushpadpinde-20&pp=0&epik=dj0yJnU9YWxPYlRvM1hvS2lZYnVDc21qSmV0bmgzZGVjdTV0RnomcD0xJm49a0pNaVpIZjBpaS1xaVVYcjJCRjgwdyZ0PUFBQUFBR2xhME9n&th=1

You don't WANT float shelves. It's too narrow. You want a carpenter, 3 sides with a shallow "french cleat", and set 3/4 inch shelves in a fixed position, about 12 inches apart , Trim the front edges, and you have a custom book case, Paint is WALL color , satin. No brackets needed.

This look......

I have a shelf in my guest room closet with some books and newer magazines no need for a ton of old paperbacks no one stays long enough to read them all. I would leave that space empty or maybe a nice coat tree with a fluffy bathrobe or 2

As Jan Moyer suggest a custom bookcase would probably look better than floating shelving.

Shelves are an easy DIY.

Thanks. We live in a tight rowhouse. The room is doubling as a place for guests (three times a year) and will be our book storage area, so I think I won’t convert it into a coatrack or bathrobe space. (There’s another bookshelf on a different wall too.) I guess the reason why I was thinking thinking floating shelves—maybe in a nice wood—was that the space was already naturally framed out, and would it look good to add yet more trim and framing within that space?

Having said that, Jan, I really like the look that you posted.

You do a Marie Kondo On the books. You limit this to hardcover. Paperbacks are donation, or if must be saved? I can not imagine why: ) Even the research information type is ONLINE.

"Float" means that. Three sides of each shelf faces .... thin air! Then...how do the books stand up? Book ends?

It's waste in a narrow space, when you seem to cling to all the books you own. I love books as well, but! A prune now and then!

Draw and measure the whole room...........show the rest of the room, all the angles from the corners !

The pic I posted is a lot prettier than a fad of the decade, float shelf. JMO. and you lose no storage! Not every book spine must be in your face, and you can do less "trim." without losing the look.

Sorry, my Dh wants all his books. He’s only reading digitally now but he wants these to stay and likes them visible. Maybe I used the wrong word with floating shelves. The width is 23 and 3/4 so I was envisioning shelves going wall to wall. What word would that be? Maybe wall mounted instead?

You can keep asking? Do I think there's a better way than what I showed? No. Because I think float looks cheap fad, and once you go full width, 23 3/4 wide? Two inches of books either side, essentially four novels that "disappear" behind that TRIM on front sides is a total NIT!!! :)

If you want me to change my mind? Show the rest of the ROOM. This is two feet of an entire space, no matter how petite that space.

I think you have abookshelf there already what is wrong with it ? I think if you can find one a bitwider that is what I would do . I really dislike paperbacks on show at all so maybe some closed storage at the the bottom for those

Thanks, Patricia. I would prefer a shelf better fit this nook. This bookcase is 15 inches wide and the opening is nearly 24 inches. I would like to use a few shelves for display items too (we just unpacked books so this is not our idea of final display). I can find bookcases that are wider to better fit, but was also thinking how I could tuck in shelves.

I simply don't understand the problem, and you won't show the room. in total.

SEE two pics

BY AND TRIM /CUT TO FIT,,,,,,,,,,,,,,be prepared to add a facing trim.....

Wayfair.........precision required

There isn't ANYTHING you're going to buy online that will be "custom" to 23 3/4 wide, by whatever height.

You're very pointlessly wringing a hand.

For all we know you could have a WALL of books, for all we know you could go around and over the door! Or around and over a couch!

but we can't see the whole of ROOM you seem to want to HIDE.......as you search beyond obvious solutions.

Otherwise, you go online to Etsy, and buy float shelves @ 30" and trim to fit edge to edge, get some brackets and call it a day.. And no....DH does not need to SEE paperbacks.

Yours would be nearly double the width of what you see below. ........

Bookshelves can be as little as 9 inches deep. Proportion matters, as does thickness of shelves. for a good LOOK.