How did getting a new dog affect your senior dog?

I have a lab who is 9 – he seems content but he’s a couch potato and I worry that he is just bored. I take him for exercise every day and do my best to keep him active and enriched. However I was dog sitting my friends dog this weekend who we used to live with and my dog seemed a bit more animated. They don’t really play together but he seemed to be slightly more engaged and drinking more water, less dragging on the leash and not wanting to walk, etc.

I used to live with roommates and this other dog so my dog had more sources of “things going on”, but now that I live alone I worry he is bored.

I’ve toyed with the idea of getting another dog so the new dog could learn from my current dog and also to cushion his eventual death for me.

Anyway, how did getting another dog (more specifically a puppy) affect your senior dog?