First Hibernation help please

[carryonsue]

Hi Ev1,
Had my horsfield Pebbles since march this year and she`s fab, was told she was 2-3 years old she now weighs about 350 grams and shell is 115 mm length is this ok or is she too fat or not fat enough lol, will it be safe to hibernate her or is she still too young ? if so when is it best to start the hibernation process and best hibernation box ie bedding etc to use, I was thinking of putting her in my loft as it keeps cool is all boarded up and no fear of rats or mice, any help would be gladly appreciated as first time will be very nervous and worrying time ha ha silly me, anyway thanks for help guys and girls.
Susan And Pebbles.