The region where this famous rice dish traditionally comes from (although eaten nowadays throughout all Spain) is Valencia, in the Mediterranean east coast of Spain.
The proximity of the “albuferas” and marshlands (which are very characteristic landscapes), made the existence of rice fields possible and set like this the perfect conditions for the creation of this dish (there are not many zones where you can cultivate rice). So as you can imagine, the rice, which the Arabs introduced in Europe 800AD, is key to good Paella valenciana. Like with sushi, it needs to have the perfect consistency in order to reveal its best flavor and texture. It might seem basic, but it is the pillar everything builds up on.
The variety Bomba is the rice of choice for the valencian paella as it absorbs much more liquid and flavors than other rices. This one from Valencia is available on amazon. You can also use any other arroz redondo (short-grain rice)
A curiosity not everybody knows is that the name “Paella” actually doesn’t refer to the food itself, but to the pan it is cooked in!