Throughout Pride and Prejudice, some characters wear either chemisettes or kerchiefs (fichus). Chemisettes and fichus were worn both for modesty and warmth. They would be tucked into the bodice.
Mrs. Bennet's chemisette: Lots of frills
Kitty and Lydia's chemisettes: Kitty has the chemisette with lots of frills while Lydia has a collar chemisette. I remembered seeing a Simplicity pattern that had a chemisette similar to Lydia's, but I think it's unavailable now. You might have to look at E-bay or other pattern websites.
Mrs. Gardiner's chemisette: Not as many frills as Mrs. Bennet's.