Alison 1

I'll add that in France, we'd add an s to pronounce it properly. Alison or Allison with only 1 s would get it pronounced alizon. Oh, and the "on" would not be pronounced "onnn" either. I doubt it was any different in medieval times, if this article is correct...
So Alison pronounced [Alison] would only work as an anglo-saxon name, they are still "à la mode", after all.

I like this name. I don't really notice the 'son' on the end. Maybe it's just the town accent or something but around where I live we all pronounced it 'al/is/en". Maybe we just can't talk right, I don't know. lol.