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The Steven State are fine if you want a closed headphone, they sound ok right out of the box but have shy treble and subbass. Their bass seem to be punch focused because of the emphasizes around mid bass. If you EQ them to a good target like the Harman Target (they don't need much), they'll be good.
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There are also other options for closed ear headphones. The Beyer 1770 for instance comes to the mind but I wouldn't get it because of the treble and a very deep null resonance inside the cup around the pinna region. On a cheaper (and better) side , you can get a Shure 840A. It will sound right out of the box and it was made with production in mind (Harman neutral, detachable one end cable and foldable/tiltable earcups):
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Also, when I talked about studio monitors I was talking about active speakers, not headphones. They're a whole other rabbit hole and I encourage you to get a pair of you still don't have one: while it is possible to mix purely with headphones, the end result will almost always sound weird on other equipment and even on other headphones.
I'm not qualified to recommend speakers, as I don't know much of the NA/EU market, but if I was forced to pick a pair, I'd recommend the JBL 305p or the 306p line of active speakers
With them, bigger often is better (bigger woofers means less distortion when playing louder). The only caveat with them is that some unit produce hiss around the tweeter when not playing music, and that hiss is specially noticeable when sitting close to them.