For a purpose-built set of open-back critical listening headphones, the Beyerdynamic DT 990 PRO is a decent option, but it’s better for mixing. It sells for less than the DT 900 PRO X and still offers a good balance of comfort and utility. One downside is that its 250Ω rating requires a headphone amp or audio interface if you want to equalize the headphones. If you have one already, then that works, but if you don’t, the nice price (compared to the DT 900 PRO X) might not actually work out to be cheaper overall.