Justin's Mom Approves of Jess!

The two most important ladies in Justin Timberlake's life—mom Lynn Harless and girlfriend Jessica Biel—have become super close since the couple moved into their $2.9 million NYC duplex — which they furnished with $25,000 worth of merchandise from ABC Carpet and Home — this month.

"Lynn and Jess seem really tight," says an insider who saw the pair at the W Hotel's backstage lounge before Justin's William Rast fashion show at NY Fashion Week.

Jess, 27, and Justin, 28, are planning to celebrate his success at Fashion Week with a beach vacation. And a second source tells OK!, "they ordered black his-and-hers Havaianas flip-flops with their initials."