I'm sorry about your loss. Losing a friend is very hard
"Natalie was nice enough to offer me a highly discounted replacement puppy"
That was very nice of her to do. With your dog being 5, I'm sure she didn't have to make that offer. (I'm not a breeder, so I don't know how long they honor a well puppy agreement) I'm glad you had 5 yrs with her. Those memories are precious!
Getting a rescue dog is a good idea too. You'll know when your ready, and it's worth looking into.