I did something similar to three stock Touring seats (the original one, the Triumph solo seat and another one I found on eBay). A local MC uphosterer created almost new custom seats for me. MUCH different than anything I could have bought for the same $$$.
About $375-400 for modifying all three seats. Well worth it so far!
I've uploaded photos of my Road Sofa he made for me. Blue marshmallow jobbie. Super comfortable with a lip rising in the back to lean up against.