Unfortunately, what you are looking for is a ... unicorn. No such thing as state of art closed back headphones that offers isolation and doesn't leak sound AND sounds like a $1000
Some here will offer the Alpha Prime by MrSpeakers as an option. But that's a mod, a severe mod that makes it seem like a whole new product, but in essence still a mod, and it has severe variation problems in the production line, not something to take chances with using big money. Just don't go this path.
There is an unproven Audeze EL-8 closed back, which you must await reviews and impressions for.
Fostex TH600 and TH900 offer really minimal isolation, and leak a lot of sound, so they act more like open back than closed back headphones.
LCD-XC is probably a very good bet, although if you are sensitive to treble spikes, I'd advise against it. It is also 1.5 pounds, so quite heavy (more than twice your current closed back).
An interesting option is LFF's Enigma, and the less known Enigmatic headphones, which are entirely handmade by one person (Luis) and are custom tailored to each person, and use custom drivers (they are not mods of other existing headphones). If I wanted to buy a closed back in the $700-$1200 range today, that actually worked like a closed-back headphones, these two is what I'd look for.