Assuming a person has something approaching normal size hands I cannot figure out why anyone would want to make their pistol “fatter.” After a certain point the wider the grip, the harder it is to hold onto. Since the grip sleeve isn’t actually affixed to the pistol (except by its own tension) they are susceptible to turning and shifting, especially in hot climates. Moisture has a tendency to get beneath the sleeve and the actual grip panels. On metal framed guns this can promote rust, and any grit that gets between the sleeve and the frame can grind through the finish. Rubber grips also tend to stick to clothing more than wood or plastic.
If you really need a “fatter” a grip then replace the grip panels, but for most people this isn’t really necessary. I replaced the grip panels on one of my 1911s in favor of panels that were even slimmer than stock. If a single stack pistol is too slim for your hands then why not get a double stack gun?