I would consider a quality knife custom made to fit properly in your hands. i also have issues with my hands and raising the saddle/yoke helped me out. But, I must say that maybe making sure your knife blade is super sharp would be a good start. This would come from a quality blade. I find that newbies tend to use the SK improperly. The pressure comes from the top of the saddle downward. The fingers around the barrel turn the barrel for turns. Every part of the operation of the SK moves in with the help of each piece. The biggest issue I hear from newbies is the cramping of the fingers surrounding the barrel. I usually find that they are putting the Kung Fu grip on the barrel.
I start with sharpening the blade and go over the basics with them. That usually corrects most issues.
In your case, if you have been cutting for a while, I would definitely consider contact Barry King, Leather Wrangers, Hackbarth or even Clay Miller to see about having a larger barrel. Try different sizes of instruments to see what size you would need before you order.
I hope you find a solution to your issue. Good luck