Being an owner of both Dachshunds and Labradors I will do my best to help you with this. These are the questions you need to answer:
1) Is my 9 year old Dachshund dog friendly?
2) Is my 9 year old Dachshund active?
3) Does my Dachshund have any arthritis, back issues or overweight?
Because:
1) A large breed puppy (such as a Labrador) is very playful, nippy and has no idea how much they weigh or that he can hurt or even seriously injure an older Dachshund.
2) The puppy will want to play, play, play. If the Dachshund does not want to play, play, play then the puppy will become a nuisance to your existing dog.
3) A Labrador grows fast. A Labrador usually retains it's high level of activity for years; the need for serious exercise every day including obedience training.
What you have to decide if this is a good thing for your older small breed dog and for YOU.
Think it through.