My GF has scoliosis as well, and was never able to spend long hours on any of the bikes I've had over the last ten years (including an '83 Gold Wing I had for a while) due to back issues. That is until I got my '89 Ultra. I had the stock seat redone, rider and passenger cushions, by Mean City Cycles. No complaints since.

 

One more vote for the mustang. When the wife rides with me I put the wide super touring seat on my Heritage. She says it is makes all the difference in comfort.

 

When it comes to wife's comfort, the wider the seat the better on the longer rides. All good suggestions already provided. I would suggest taking the bike to a dealer either HD or Indy and sample a couple with her present. I replaced the stock EG seat for a stock road glide seat. I like the look and it feels great for me on long rides. Wife says she can live with it, thou not as compfy as the original seat. The sheep skin is a huge favorite too.

 

DH's first bike was a Dyna: he never let my throw a leg over it. His sister in law went for ONE ride with his brother and said "never again". No way he was going to risk that, so he did his first season solo, then traded up to an Ultra. It had a W I D E seat for his wide wife. It also has buttons on the upholstery, no matter what we tried, those damn buttons poked me, so we decided the ashtrays were full..... and traded for a new one!
We do long tours, as much as 6 weeks at a time, full days of touring, I need to do my part and sit. We use a stock seat, toss on the sheep skin, the big improvement has been my passenger highway pegs. I can vary the stress on my hips and pelvis. Happy Wife, Happy Life.

 

Mustang here, wife loves it. Got the wide touring 1pc for my FLHX, we've got 6-7 hour rides with nothing more than a leg stretch every hour or two. Like was mentioned before, stretching your legs every now and then REALLY helps. Adjustable foot pegs sound like a sure win.

 

I just ordered a Mustang seat, when I get her on and get riding I wil let you know what I think. It can't be worse then the seat that came with the Sportster!!! I don't know if I will ever walk right again!!