I have the exact same set up. That pillion has a little wiggle to it until you put the backrest in. I wouldn’t put my wife on the pillion without the backrest installed
808-07B-0042EXT - seat, 808-07B-0142L - pillion. That’s from saddlemens website. Just double check the seat to make sure it’s not the low version. I would use Denniskirk or a website like that, they have better fitment guides.