MARTHA Stewart has lost so much weight in jail, she needs a whole new wardrobe. The domestic diva has dropped close to 20 pounds due to workouts, yoga and her inability to eat prison food — so she sent daughter Alexis to get her some clothes to fit her new, svelte figure. Alexis and a Bergdorf Goodman personal shopper were "ostentatiously" perusing the racks last week for size 12. "They decided on a $3,980 suede jacket for Martha," said our spy, "among other things. I guess it will be Martha's 'coming out' look." Stewart gets out this weekend. (Page Six)