Currently, I am using an ESP8266-05 module in my IOT Projects. I am planning to switch to ESP8266-12 module as it seems more PCB friendly (robust to industrial environments). Apart from the small changes like(extra GPIO pins), will there be any changes in the AT Commands set or bands in which the module will work?. I tried but could not get any official module specific document/Comparison for esp8266-12
No, the official SDK and all firmware (e.g. NodeMCU, Arduino) are identical across all modules because the chip itself is the same.
Maybe https://frightanic.com/iot/comparison-of-esp8266-nodemcu-development-boards/ and https://blog.squix.org/2015/03/esp8266-module-comparison-esp-01-esp-05.html will help you pick the right module for you.