I have been researching saddles and the impact they have on the horses back, and to this end decided on a treeless saddle. After further research and seeking of opinions and recommendations I ordered an ‘Atlanta nut’ from Barefoot Saddles.
They are considerably lighter and have a flexibility that allows the horse to move naturally with you and the saddle. It took a little getting used to (a deep seat is very helpful in the first week or so) and you need to allow it to settle and shape itself to your horses frame, but once it does they are very comfortable for both horse and rider.
For further insight into the science behind these amazing saddles please take a look at their research information.