He's been here a week and a half. I'm sure I'm gonna get flack on here about bringing in another bird already. They'll be on separate floors.
I'm honestly not interested in how soon it is that you get another bird. It's just your reasoning.
You haven't given the senegal a chance to bond with you at all and you're considering getting a sun to be your bird because of it.
Now back to the question;
Your sennie will not take to having another bird around nicely at all, doesn't matter if they're on separate floors - your sennie will know there is another bird in the house and he will get angsty about it. You have uprooted this senegal (bad situation or not) and not given him enough time to even settle and begin trusting you BOTH before introducing a conure into the mix. Your sennie will have all sorts of issues:
he'll want to learn to trust you, but wont do because he'll be confused with all the jealousy he's experiencing. So instead, expect bites, lots of them. and mood switches, lots of them.
He'll want to be a cuddle bug to you, but as soon as he'll hear that conure screech, he'll be put on edge. Probably bite you and fly off. He cannot see this bird, which will make him anxious as it's something that sounds familiar (and so should probably be part of his flock) but he doesn't know that bird. If your conure is calling out to you because you've left it upstairs, your sennie is going to pick up on that stress and presume it also is going to experience stress...
If you have one bird upstairs and one down, how do you expect to split your time? One bird is going to feel left out, or you and your partner arn't going to spend time together as one of you will have to be with their "own" bird.
Your conure will be fine if you bring it home.
Your senegal will not.
I'm sorry, I'm all for bringing another bird into the mix, especially when one hasn't bonded to you.
But; you haven't given the senegal enough time and you don't know that the conure will do the same.
Bring another bird home when you're confident and comfortable that you will love both equally, spend equal amounts of time with bonding, training.
Not just because this is the species you want and the other bird you have hasn't worked out in a short amount of time.
Just my 2c; sorry if you don't like it. I'm all for the birds interests, not sparing feelings. Give it a year or so, then if your senegal still has no interest in you and you still want another bird for your own consider bringing a sun into the mix after you've met it, bonded some, etc.