I am not concerned with look, but with the fact that I take him trail riding at least once a week and we always go through a river that in some spots is deep enough that my saddle is completely sumerged and at the lowest spots at least the bottom half of my saddle is getting splashed, and I need a saddle that won't get damaged when wet as a leather one will.
Then Wintec or Thorowgood are it. Have you tried a Thorowgood on him?
What are you feeding him? Is he gaining weight? Have you dewormed him lately? If so, with what and how often? Has your vet been out in the last 6 months to check his teeth? He needs to gain weight and muscle, and his coat looks a tad dull. You might consider looking more closely at his diet.
I would have him on free choice grass hay or timothy hay, 1-2 scoops (3qt feed scoop) of Alfalfa pellets, and a custom blend from horsetech.com of: NutraFlax (2 oz per serving), BioFlax, Yeast, and Probiotics for a 4 oz serving (should cost about $90 for a 20 lb bucket, which would last about 3 months). This, along with his normal grain or a vitamin supplement, will round out his diet, add quality calories, help him gain good muscle, and improve his overall condition.
As I posted over on HGS, I also think you could really use a Skito Correction saddle pad
. He's a great candidate for the long shoulder bridge shim. That worked wonders with my TB cross gelding who had similar wither issues. It will help fill in for the lack of muscle and topline, so you can get a "normal" width saddle and allow his muscle to develop. Once it does, you can remove the shims and ride with just the base foam as a "shock pad", to keep his back comfy and cool. If you go with 1/2" base foam, it won't change the saddle fit once you remove the shims.
A riser pad changes the fit, which may cushion, but will ultimately make him uncomfortable with the extra pressure behind his shoulders.