I use a soft-sleeve, top-loader, and team-set bag for my better cards. If you use just the soft-sleeve, an accidental bump can damage the card. If you use a soft-sleeve and top-loader, the top-loader protects the card from bumps, but gets scratched up over time, which I hate, so I use a team-set bag over that to keep the top-loader clean and scratch-free. The team-set bags are resealable, and keep most dust out too, meaning twenty years from now the tops of the cards that are exposed to air when just using soft-sleeves and/or top-loaders shouldn't yellow with age. I plan ahead lol
There are many, many other methods, and none are particularly cheap. Team-set bags cost about $25/1000, for instance. Top-loaders cost even more, and come in a variety of thicknesses. Still, if you have enough valuable cards and want to protect them, you gotta shell out some $$$, or your cards may wind up near-worthless years from now.
So I'd advice your next step to be buying a pack of top-loaders from a local card-shop or somewhere. Get however many you think you'll need, and try not to handle them much afterwards as they'll scratch easy and eventually you'll need to replace 'em. A shop may or may not have team-set bags...I don't know, I bought mine online...but you only really need them if you're as nuts as I am lol
I'f you only have a few cards, I'd see if the shop has old top-loaders for sale, otherwise you should buy a pack and keep 'em for later as your collection is likely to grow. Make sure to buy a pack with thicker loaders as standard loaders are usually too thin for game-used/relics.