I disagree. There are horses out there who are oddly shaped, A-Symetrical, muscle atrophy, and etc, etc, etc - where no matter how hard you try to find the perfect fit, you wont.
With my fellow, I have a horse with narrow withers, but has broad shoulders and a broad back. So I have to go with a wider tree, and pad up. He also has muscle atrophy behind his shoulders, so I have to fill in those gaps. He also is weaker on his right side than his left, so I have to fill in the right side to make it even and balanced.
Then over time, through correct riding, muscling up, lunging, I can take away the shims here and there as he evens up and strengthens up, to the point where I wont need the shims.
In those situations, you have to find a saddle that fits well, and pad up, shim up to make it fit even better.
My suggestion, is to hire a Professional Saddle Maker/Fitter to come out and help you with this. I've had a handful of Saddlers come out and assess my horse, and all have come with the same conclusion - that I have to pad up, fill in gaps and pockets to make the saddle fit.
So, that's where corrective pads come into play. I highly recommend the Ultra Thinline Comfort Sheepskin Half Pad, I just purchased this pad and I am in love <3 <3 <3
Stay away from memory foam and gel. They do nothing. When you put pressure down onto the material, instead of taking the brunt of the pressure points and evenly dispursing it....it runs away from the pressure, allowing the pressure points given, to continue doing what it does.
Look into the Thinline. I cannot say enough about how well this product works. Even if you get a basic 1/2 pad, with pockets - you can buy the thinline shims and use those.
Again, contact a saddler to come out and help you. They are the one's who are trained in this field, and can give you the best possible advice. That way, they are there in person, seeing your horse, hands on, and can then take needed steps from there.
Best of luck!