JD,
Let me assure you, that having a companion for your Dog, is something
special. There's a fellowship which they will experience (with each other)
that no human can match.
When bringing a new animal into your family, I've always said...
Same Breed, Opposite Sex, and the new dog younger than the resident,
where the older one can maintain it's seniority.
Beyond the actual placement...
One needs to be sure to give the resident a LOT of extra attention,
where it won't think it's being replaced in your heart. That's a must do !
Now, about the Spay...
You know that the procedure can be done in a very short period,
only takes an hour or so, plus a short recovery time...
AND, the scar is SO subtle, many don't even notice it.
Any lethargy from the operation, is so similar to the occasional
reaction from inoculations, one would hardly be able to tell
the difference.