Looking for an Arduino board which would help in converting 12 bit binary input to decimal equivalent

I don't see the problem. You have commands to print numbers to the OLED, just use those commands to print your 12 bit number. It will automatically print the correct number.
Does your code spend all its time converting all those digital inputs to a number? It is trivial to extend this to 12 bits.
The title to this post is very confusing, because you will never want to convert a 12 bit binary number into decimal. All numbers inside the Arduino ( and all other computers on the planet) use binary numbers. It is only when you want to print them out that they are then converted to decimal, something you don't have to worry about.

Post the code of what you have at the moment.

You may want to read this before you proceed:-
how to get the best out of this forum

It will, amongst other things show you how to post code.