Jennifer Lopez's search for a new post-Ben Affleck home might be over, but she's holding off on pulling the trigger just yet due to L.A.'s wildfire disaster ... TMZ has learned.

J Lo recently toured a $20 million off-market mansion in Brentwood ... according to a source with direct knowledge. Of course, that's the same L.A. neighborhood where Ben purchased his new home after they split.

We're told Jen "really likes" the home, but has "serious concerns" about the air quality around it. Remember, Brentwood was affected by the deadly Palisades Fire right next door -- many residents there, including Ben, were forced to evacuate, and the air quality is still pretty poor.

We're told J Lo is pulling out all the stops ... she likes the place enough to bring in an air quality specialist to test the area before going any further in the purchase process.

Jen and Ben are still trying to sell the L.A. mansion they bought together while they were married. It's on the market for $61 million.

Think about it ... if the air's right, J Lo and Ben could be neighbors again.