There are many good book shelf speakers. Look for one that matches your amplification and source and cables. You have plenty of bass so if it were me I would want a speaker with a reach midrange.
Lots of good monitors out there so I am sure you will get lots of advice.
Don’t forget to take a look at thin tower speakers too. You might find they blend better with your subs. Sometimes when playing high volumes the mid bass lacks when handing off large subs to small bookshelves. The scale just seems off somehow. Maybe something like the Revel 226be if you are not dead set on monitors.
@yoby , just this weekend I heard a pair of Dynaudio Heritage Special loudspeakers do a surprisingly excellent job of casting an image while sounding totally neutral. They reminded me of the LS3 5A but with more bass. They are within your price range. IMHE only Harbeth makes bookshelf speakers of that quality. Since you are using a subwoofer the Harbeth P3ESR XD is another option and less expensive. Do not let the small size of these speakers fool you. The Dynaudio has a ferro fluid cooled tweeter. With a subwoofer and a proper two way crossover they will play as loud as any large point source speaker.
@grinnell I have a small REL sub with my de Capos, crossover set pretty high. They blend seamlessly.