If you just want a small, simple box then don't bother with Leo Bodnar's controller. The difference is only in the number of inputs you can have and I only needed the controller since I was also inputting my joystick and rudder pedals. You can even increase the number of inputs from a single controller by doubling up inputs (e.g. command 'O' is different to 'Ctrl+O',
see here) if you are willing to do a bit of hard work double-wiring each input. You can do this with any controller.
If you want to do it the simple way then something like this will work. My control setup houses the BU0836X controller inside this little black box (and, yes, the cup of tea is obligatory):
The advantage of the Bodnar controller is that you can have six axes (the sliders on this box and x/y-axes on the stick and z-axis on my pedals). If you already have a stick and pedals set up then you can just add more sliders or trim wheels.
A big advantage of the Bodnar controllers is that you can also have rotary encoders (the yellow knobs). These effectively convert rotation into button inputs, so each click as you turn equates to a single button press. Very good for trim control which is what my three are used for. One rotary encoder uses two controller inputs. The buttons are just one input each and the switches are one input each pole.
The slider on the side of the box is prop pitch and, working left to right, the others are throttle, mixture, radiator, and carb heater/supercharger/oil radiator depending on what I am flying. The rotary encoder on the side is elevator trim and the other two are rudder and aileron trim.
I have an old printer cable coming out of that control box and into the stick and rudder pedals but this could easily go to a second control box instead. The cables exit the bottom of the box through the desk and you can see where I have cut the desk up to allow the joystick to move forward without sitting too far back.
(See my sig for stick info)
One thing I would comment is that after I spent a lot of effort making a larger control box I found that I was routinely only using about a dozen buttons. Out of 250 possible inputs... A smaller box was called for so I redesigned to the current one which just uses the standard inputs from the Bodnar controller. Perfect!