Places like Target and Walmart sell deck protectors (it's what those nice card sleeves are called) for about 5 bucks. And you get enough of 'em to sleeve all your cards in your deck (60).
However, I would suggest that you also slip them into penny sleeves for a little extra protection. Sure, deck protectors are fancier than simple penny sleeves, but they can really warp your cards because moisture can get inside the sleeve, and stretch and expand the cards. You'll notice this because the cards will develop a progressively bad and noticeable "bow echo" when picked up. This can be countered by putting the double sleeved cards (penny sleeves first then into deck protectors) into an additional layer of protection; of which being a basic 3-ring binder with the 3x3 card sleeve sheets.
If that seems too much for you, and especially considering you're going to be playing the Pokemon TCG casually; the binder is not necessary for card protection. But yeah, double sleeving your Pokemon cards should help you out, and minimize the amount of damage that outside forces can place on your cards.
Just remember to keep them in a cool, dry place. They're kind of like sugar and flour in a way. They all don't do well when exposed to moisture.