I use universal style canvas saddlebags. Take a look at the picture on my web site. Please don't look at the word "Yamaha" on the side of the bag. I need to get out the Magic Marker.
These bags, like most aftermarket univeral-fit saddlebags, have lots of adjustments. The two bags velcro to each other, so I adjusted them so that there is canvas across the passenger's seat, then the bags hang on the sides. There are four straps that connect to the footpegs and license plate light. You can connect them to whatever works for you.
The passenger sits on the canvas part. It's like having extra padding on the seat.
The only problems I had were:
1. The rear turn signal stalks were in the way. So I took them off and put the turn signals into the empty pods beside the brake light. This is a Ninja 250R.
2. I had to have the bags pretty high to avoid the mufflers, but then they wouldn't hang flat. I took out the plastic liner in the bags and, "shazam!" they fit great.
I think just about any aftermarket saddlebag could be made to fit reasonably well. Your passenger may have to sit on the straps. Some bags have a heat shield on the bottom. Mine were on Ebay, and cost me $47.32 including shipping.
Curt