I believe it's doable! Especially since dogs come in all different energy levels and personalities, even of the same breed.
Scottie was around the same age as your yorkie when I considered getting a second puppy. I was super anxious about it! He was still very very playful at that time. Once he hit 2 years, at which time we brought home Casie, he had already settled down quite a bit.
Not sure which of mine has more energy, but Scottie loves standing - his preference is to stand rather than relax and lie down. Casie, despite her bubbly puppy energy level, is kind of a chill puppy - her preference, whenever not much is going on, is to sit or lie down. Given their age difference, I think Scottie was a much more active puppy than Casey is. Anyway, point it, I don't think it matters - they get along great even though they're completely different!
