Firstly, pregnancy and whelping are not covered by many pet insurance policies. Check yours, and if it’s not then you might have to switch (would you lose lifetime cover?) or check you have at least £7k in accessible savings
You need to find out what health screenings are recommended for the breed and get all of those done (not covered by insurance)
Then you need to select a mate - who needs to have good complementary scores on all the tests. Also you need to ensure a good COI (avoidance of inbreeding)
Read up on what is involved in care of a pregnant bitch, for whelping, and care in the postnatal period and of newborn puppies
Decide if you are really up for it. Have you really got the space and the time?
As your bitch is elderly in breeding terms, then you’ll probably need to do the testing and book the stud ready for her next season,
The other extremely important aspect is how you will find good homes for your puppies, and how you will vet candidates
Have you spoken to any breeders about the nature of the commitment? Good breeders offer lifetime support and returns. What would you do if a puppy is returned? (Well bred puppies are rarely returned from good homes, but shit like divorce/bereavement happen and you need to have a plan)
The cut off maternal age for KC registration of puppies is 6
And remember that you will not necessarily cover your costs if the litter is small, stillborn or sickly.
Also that your bitch’s temperament and health might change (maternal death is rare, as long as you can afford a C-sec and your vet is a good surgeon)