I have a Sig 228 and short, fat, arthritic, saussage fingers that presented me with such the same situtation.
What i found was that there aren't (that I know of) any grip panels available thats appreciably thinner than the OEM plastic. Wood can't get much thinner than OEM plastic w/o risking spilts or cracks.
That said, Hoage can use a 'take-off' set of smooth plastic grip panels and checker them. Using a tape measure, there isn't a measurable difference in the girth. The reality is though, the 'felt' reduction in girth with the checkered grip panels is significant. The cost, if I remember right, was 45.00.
A visit with the folks at a Sig forum may offer other suggestions, but thats the best that I have found.
salty.