Big changes are ahead for Westfield Montgomery mall once the holidays are over. The deal with Life Time Athletic, which we told you about two weeks ago, is all but official — and we hear it’s going to be quite an upscale gym, with a formal restaurant and possibly a rooftop pool. The new Life Time is to be built on the Sears side of the mall after the ailing department store closes early next year. Meanwhile, we’re hearing that the Macy’s Home Store is also going to close this winter and the regular Macy’s store will have to absorb all that furniture, bedding and kitchenware. But it sounds like the squeeze will be temporary: Insiders tell us that Macy’s is planning to build a huge new store on the other side of the mall. None of this has been announced yet, and no one is talking on the record —  but you heard it here first.