Power converting - up or down?
Since your project is to be battery powered, you want to make your system as efficient as is reasonable.  

So I am going to take an approach that ends up improving the efficiency of your project.  

The button you describe in your link states :  


  This button has a domed red plastic cover with a black retaining ring around it. There's an optional LED included  


Further, the LED included has a "built in resistor", so that the LED can operate from 12 volts. 

Since you would have to install the "optional LED",  why not purchase a Red LED that operates from lower voltage. You will still need a resistor but you won't need to have a voltage converter.  

Example  :  Their LED probably has a 2 volt LED (approximate) that operates at perhaps 20 mA).  This would require a 500 ohm resistor (which they incorporate into the LED).  The power loss (wasted) in the resistor is 0.2 watts (200 mW).  

Improved Example :  With LED of about 2 volts operating from 3.3 volt power source.  This would require a 68 ohm resistor.  The power loss in the resistor would be 0.027 watts (27 mW).  A substantial improvement in efficiency.  

The manufacturer of the button does not give specifications for the LED (the one with the resistor included).  You should connect their LED to a 12 volt power supply and measure the current drawn.  It is possible their LED draws more current than I have shown in the examples.  This would require a re-calculation of the resistor values.  

But in any case, the improvement in efficiency will still exist.