Here's what I did:
In Windows, I added a second keyboard (Spanish (Mexico)) to the existing Keyboard. A previous answer points to an article by Microsoft on how to do this. I took the option that facilitates switching back and forth, using the Alt+Left Shift combination of keys.
I printed myself a cheat sheet that shows the layout on paper, just in case I forget where the Spanish keys are. (Heck, I don't even remember where all the keys are on the English keyboard!)
Here's an image of the cheat sheet:
Esto es el teclado español.
1a fila: ° ! ” # $ % & / ( ) = ? ¡
| 1 2 3 4 5 6 7 8 9 0 ’ ¿
2a fila: Q W E R T Y U I O P ¨ * ]
q w e r t y u i o p ´ + }
3a fila: A S D E F G H J K L Ñ [
a s d e f g h j k l ñ {
4a fila: Z X C V B N M ; : _
z x c v b n m , . -
Arrobas (@): Ctrl+Alt+Q
El acento es tecla muerta.
The cheat sheet lines up correctly in my original, but I can't make the SO website line it up right.