Stove Top Heat Diffuser in BKK?

Looking for a heat diffuser for my electric burner in BKK. The burner is about 7" (18cm) across. My pan is about 10.5" (27cm) in diameter. Looks like the large size commercially available ones are usually 9.5" (24cm) wide, which would probably be fine. Some are stainless steel plates, some are cast iron. Anyone see something like this available in Sukhumvit area? Actually, I've seen guys using a thick sheet of copper for this, so that could work, too. Thx.