Ah ... a subject I am now an expert in
I too like to sit back. I discovered eventually that a lot of my discomfort was I was actually sitting on the back ridge of the seat. I have extended floorboards as well.
I tried stock ... no no no
I tried stock with gel pad ... better ... only no no
I tried Mustang with back rest ... no way ... felt like I was sitting on the tank. Took the backrest off and I ended up sitting like i used to and sitting on the backrest bracket insert was terrible. no no no no no no
Tried the Corbin. Sat "okay" but felt like it was a concrete block. This was a friends seat that had 10,000 on it, so I am sure it was broken in.
Tried the Ultimate ... ah ... sitting on a cloud. I sat back a bit too far still, but once it was broken in (about 1000 miles) it was so much better. Put a backrest on to FORCE ME to sit right and I can ride tank to tank to tank with no problems. A short trip for me is 300 miles, so seat comfort is critical. Very happy with the Ultimate seat and with the service they provide. MAKE SURE you tell them you want the backrest bracket in the pillion seat. That way if you decide you want to get one, you just buy it and put it in. I also run a sheepskin and on hot days I am much more comfy and cold days warmer.
I have ridden on Russell Day Long Saddles as well. My next bike may get one of those, but the Ultimate on my R* is great.