Britney Spears signs a wall of the Britney Spears Foundation Room at Boston’s Onyx Hotel 9-15-04

September 18 2004, 3:35 pm

Pop tart Britney Spears finally checked out her palazzette at Boston's Onyx Hotel yesterday, quietly slipping into town with fiance Kevin Federline after her much-ballyhooed Big Apple perfume launch.

``I can tell my mother designed this,'' the oft-barefoot songbird said as she walked through the door of the $259-a-night Britney Spears Foundation Room and bounced on the bed. ``It's got my mother written all over it.''

But it was Brits - not mum, Lynne - who signed the wall of the 10th-floor room decorated in soothing tones of beige and sage and outfitted with photo of Spears sporting a halo and a bra.

And Lynne's kid recognized one of the fairy tchotchkes in the room's curio cabinet as a previous inhabitant of her childhood bedroom in Louisiana. (A portion of The Foundation Room revenues are donated to the annual Britney Spears Camp for the Performing Arts on Cape Cod and other Foundation activities.)

After the future Mrs. Federline's quickie look-see - a tour she's been scheduled to take since May - she fled Boston at 3:30 p.m. on an American Airlines flight back to La-La. We hear Brits reserved the entire first-class section.

Why? Because she can!

Meanwhile, Mama was back home pounding out a missive on Brits' Web site defending her daughter's right to walk barefoot in public rest rooms and wear trashy clothes! Lynne blames Brits' penchant for walking around shoeless on her recent knee injury.

``The doctor's orders are for her to wear Uggs or tennis shoes and it's just too hot for that,'' wrote Mama Spears. ``Sometimes, it just feels good to go barefoot in this heat and give her feet a rest.''

But in a public bathroom??? As Teresa Heinz would say: Ick!

And as for her affianced daughter cleaning up her act, ah, don't count on it, says Spears mere.

In other words, What U See (Is What U Get).

``My daughter is not one that is going to give into the pressures of dressing up every single day in order to impress the paparazzi vultures that await her outside,'' she wrote.

Because her Baby, Baby, is no Slave 4 Fashion!