All birds are individuals. My green cheek is much quieter than my senegal. Additionally, I find her voice less piercing, but people's tolerance to noise is also varied. My linnie is also louder than my senegal, so what can I say?
My son, on the other hand, has difficulty with the sounds of the senegal and doesn't have a problem with the linnie or green cheek. It has to be the pitch.
As Jenny said, if you already know you can tolerate the pitch of senegals, the pois seem fairly safe, but know that the larger pois are significantly louder than the smaller ones.
My parrotlet has a totally different quality of voice than the senegal. Not high pitched at all, more raspy, even more raspy than the green cheeks. If raspiness sets off your migraines, that would be a problem, because he likes his voice, a lot. It is a good thing for me that the tone of his voice is actually less offensive to me than the tone of the other's voices. He is kind of loud, but the pitch just doesn't bother me at all.
If I were looking specifically for a pleasant sounding bird, I'd go with a bourkes, scarlet chested (aka splendid), turquoisine. I love their vocalizations. They could make their calls all day as far as I am concerned - but they don't.
African greys don't scream. Even their clicks are louder than a senegal's clicks, but they don't scream. Ashlynn's voice is easily heard, but usually she is making some interesting noises. However, they can pick up imitating anything, so there is always the distinct possiblity a grey would imitate something that bothers you.