Priority number 1 is being as far away from the pollution as possible, noting also that the accomodation budget will not be much higher than 15k per month (33k salary). What can you get in discovery bay for that price?
Oh well, as long as you're not being unrealistic...
Rent a cheap pad in TC. If you're willing to live in HK on a monthly budget of 18k (good luck with that), I assume you have no wife & kids. In which case DB has nothing for you (it wouldn't anyway).
But if you're serious about it I suggest pitching a tent in the mountain somewhere behind the golf course, far enough that you won't get evicted by the guards of course. Nice views from up there...
Maybe a cheap flat in Mui Wo?
PS: You can't get away from the pollution anywhere in HK.
PPS: Welcome to hell.