Need a Large Leather Grip

I have a new Wilson BLX 90 that I got in a 4 1/4 size, but I want to slightly increase it. Are there leather grips that are thicker than the Wilson leather grip so that I can increase the size? How thick is the Wislon leather vs. other leather grips? And, how much will a thicker leather grip increase the grip size?
Ah I see. So, do you know how many mm a grip should be to increase or decrease a grip by 1 size? For example, if I am using a 4 3/8 that has a Wilson leather grip (which you say is 1.8 mm) and replace it with the TW thin, 1.3 mm leather grip. Will that make my 4 3/8 a 4 1/4?