Introducing a new puppy to an older dog, your experiences?

We lost our dear Sandra just over a month ago and 10yr old Bill is lost without her as he used to follow her everywhere. He is adapting but really needs a companion, he hates being alone. He was 5 when he came to us 5 years ago via a friend and Sandra accepted him immediately. We would consider adopting another older dog, possibly less stressful, but OH is determined to have another Spanish Water Dog, another girl and adoption opportunities are scarce.
I have read all the advice on introductions, boundaries, space for him to retreat etc., but would be interested in your personal experiences. He is pretty laid back for an SWD as they can be nuts, but still, he has strong territorial guarding instincts. Is it fair to expect a 10yr old to accept a rambunctious puppy?
Bill:

I have read all the advice on introductions, boundaries, space for him to retreat etc., but would be interested in your personal experiences. He is pretty laid back for an SWD as they can be nuts, but still, he has strong territorial guarding instincts. Is it fair to expect a 10yr old to accept a rambunctious puppy?
Bill:

Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
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I wouldn't put them in an enclosed space at first. Make sure the adult dog has an easy exit route. Make a fuss over the adult and feed him first for a while so that he knows he hasn't lost his place in the pecking order
Crate training is hugely valuable. If Bill isn't crate trained, at least do it with the pup so he/she will sleep in a crate, which gives Bill time to move about without a puppy swinging on his ears.
There's a really good book called 'perfect puppy' by Gwen Bailey. I've not looked in there for advice on this specifically but I expect she's covered it
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Bill has such a sweet face, I hope you find a new best friend for him
Wisdom is not putting it in a fruit salad.
I think dogs that are used to company will often be fine together straight away. Even solitary dogs are normally really well behaved with puppies and know how to control their play with them.
The friend he came from was a breeder who had to give up all his dogs for personal reasons. He is asking around his old contacts re older dogs and put us in contact with other breeders he knows well, so we’ll see what comes out of that.