Hi, I'm sorry to hear about Martin's death, it's always hard to lose a loved family member. As for when the right time to get a new companion is, it's when your heart tells you it's the right time. Some people get at new puppy or dog within a week, others take much longer to be ready to open themselves to this adventure again. I don't think there's any right time for everyone, just when it's right for you.
The breeder we got our first lab from suggested waiting until he was at least 2 years old before getting a second dog so there's time for him to get the time and attention and training that he needs. So Coco is old enough from that standpoint to bring home a puppy. You could also consider a slightly older puppy or young adult dog. I wouldn't go for a dog very close to Coco's age, probably at least 2 years younger, so they're both playful and full of energy but both dogs don't reach their senior years at the same time. Hopefully they'd both live a good long time and both of them would eventually be seniors together, but a bit of space between them might be easier since, darn it, they just don't live long enough. I would point out that not all dogs become fast friends so you shouldn't expect that Coco will necessarily get along with the new addition the same as she and Martin got along. But she would have a buddy to play with sometimes even if they weren't snuggle buddies.