Bookshelf Recommendations

B&W Matrix 805's.  oldies but goodies.

At your price point, you might consider Axiom Audio M5HP 3-way bookshelves.  (under $1000).  They're more than adequate for your space, although could be considered "overkill".  They're reasonably sensitive (91dB/1w), but can handle lots of power if loudness matters, or if room size changes.  So may not have to upgrade for a long time...;-)I own 7 of them in HT and Stereo systems and have been very pleased with their performance.

My son bought a pair of Axioms, back in the early 2k's [don't recall the model]. They have certainly served him well.

Forgot about those...

I've been wishing I had a good friend that was looking for a pair of bookshelf speakers so that I could turn them on to these!  There is a listing in the other "audio mart in the US" (hint) for a pair of Thiel PCS bookshelf speakers.  These speakers are unbeatable for all of $900.  If I didn't already own a pair they'd be gone, but I do, and they're not.
These speakers are "world class" speakers, especially if you drive them with tubes!  I couldn't recommend these highly enough.  I've been trying to concoct a reason why I need another pair, but I can't come up with any valid reason.  So, go get them before someone else comes to their senses.

A lot of great options mentioned. I suggest you audition before purchase if able. There are great deals to be had on the used market but I’d avoid going that route unless it’s quite obvious the speakers can be easily flipped.

 In theory, your square room is an acoustic nightmare, which means an in-home audition is your best bet for long-term enjoyment.

 The factory-direct brands (Ascend Acoustics, Zu, Omega, Buchardt, etc.) tend to offer generous, no-hassle, money-back guarantees and trial periods. Their product value also benefits from cutting out the middle-men. I think that’s especially true concerning the $1K price range.

Another speaker you should consider is the Seas A26 Kit from Madisound. Total price per pair with pre-assembled cabinets (for the U.S. market) comes to $1224. All that’s required of the buyer is some very simple assembly that any caveman could handle. If their drivers were sold individually, they’d account for about $841 of the cost per pair. These same drivers are used in some speakers that retail for over $10K. The speaker has a front slot port which will allow for greater flexibility in placement - a must in a 12x12’ room.

https://www.madisoundspeakerstore.com/2-way-speaker-kits/seas-a26-10-2-way-kit-pair-based-on-the-classic-a25/