Thanks, Greenwich Boy. I got my 30-day extension from the Central Festival immigration office this afternoon. I arrived at 3.00 pm and was out by 3.50 pm. I would have left sooner had the girl at the front desk not quibbled over my photograph saying I no longer looked the same and insisted that I take a new one. The photograph that I had provided was the same as the one used in my passport, taken about 6 months ago. My hair has grown by about 6 cm since then but I look pretty much the same. She insisted that "your hair now long, you take new photo." So I quickly pulled up my hair and tied it in a bun, showing my face without any obstruction whatsoever. She wasn't convinced and repeated, "Your hair now long, you take new photo." I gave up and went across the corridor to have new passport pics taken. Four pics for 150 Baht. The girl at the front desk was happy with the new photograph.
I don't know what I'm going to do with the other three pics. They won't be accepted in my home country as I was wearing a white blouse and standing against a white background but apparently a head without a torso is perfectly acceptable in Thailand. 😅 Anyway, all's well that ends well. Thanks to everyone who responded to my questions. By the way, the documents required were exactly as DrJack54 described. The TM7 form can be obtained there.