Youre getting a couple of things mixed up. Single walled and double walled baskets are as they sound. Most good coffee machines use single walled baskets and rely on the user to adjust the grind, dose and tamp to control the extraction.
With a double walled basket the inner wall has lots of holes (just like a single walled basket) but the outer wall usually has only one or two holes, and the result is that all the coffee is forced through the tiny hole.
Cheaper machines use double walled baskets because the extra pressure forces a crema of sorts out of the often cheaper beans/stale grounds put through the machine.
On the other hand, you might be interested in getting a quad shot (not walled) basket for your Silvia, which basically means a single walled basket that is much deeper than the standard basket that comes with the Silvia, so you can literally fit more coffee into the basket (so double the amount you can fit into a double).
The extra coffee means you can have your Silvia pump the same amount of water for a double through twice the amount of coffee, which may result in more bang in your shot.