Congratulations on your new-puppy-to-be! If possible, have Sweezy and Ellie meet on neutral territory. This might be a challenge with a tiny puppy whom you want to protect from exposure to public areas. If so, maybe pick a sort of neutral part of your home, somewhere that isn't Sweezy's favorite place to hang out.
Let the dogs greet each other on the floor without you holding them. Stay close by and alert. Don't interfere unless things look dangerous. Let the dogs work things out on their own.
Give Sweezy a place to escape the puppy. When I brought Teddy home, he was 8 months old, but too small to jump on the couch. Max retreated to the couch when he was tired of puppy antics. Make sure to continue with Sweezy's daily routine and habits so that he doesn't resent the new puppy.
Be confident, even keeled, cheerful but not overly animated. As you know, dogs are in keenly in tune with our feelings. They will react to our anxiety.
Try to engage Sweezy and Ellie in simple obedience/trick training at the same time. This will help foster togetherness.
The details you will have to sort out based on how they get along. I had to use a baby gate for meal time separation for a couple of weeks until Teddy learned that he had his own bowl. We had to establish beds and sleeping areas.
Sweezy may surprise you and fall in love with Ellie from the start.
