I have them manufactured in China because I need ESP12S with FCC ID printed on top for FCC compliance, but you can use any of the ESP12E that are common. I can’t make sense of the various model designations out there.
The PCB should be 1" wide and the pins 0.9" CC.
The serial interface chip should be CP2102, which allows much faster flashing and 115,200 baud serial link.
Here are two. You can see the square CP2102 right behind the USB socket. The one on the left is an ESP12S as used in production, the one on the right I probably bought on eBay but would work fine.
