You should mail in the 8949 that TurboTax generated.
TurboTax will create the Form 8453 after you go to the File section of the interview and select e-filing. If you don't e-file, you don't need Form 8453 because you attach the backup statements to the return when you file by mail.
In your case I would mail both. Usually, you do not really need to mail Form 8949, but you do need to mail your supporting statements, such as your brokerage statements (Form 1099B) and Form 8453.
