I often take 1.5in plugs as warmup and then use 1.75in or 1 and 7/8. The largest I take infrequently is 2in. These are diameters. The 2in one feels VERY big and takes lots of warm up. Would it be safe to try a 2 and 3/8in one?
With a lot of warm up and lube, and plugs in incrementally increasing sizes, I don't see why you couldn't try it. It will be safe as long as the plug has a flared base and you use appropriate lube and are patient.