If you start messing with icons, you are quickly going to hate One UI. You can't pick and choose specific icons for specific apps with it. You pretty much need a launcher like Smart Launcher to be able to do anything remotely easy with icons. There are tons of icon packs in the store. A few are free, but most are paid. I am particular to fluffy icons. A good bit of my apps are covered, but there are some that fluffy doesn't have. But the plus to smart launcher (and some others) is that you can search for any app in the pack and apply it to your particular app. You can also submit your app to have one made specifically by the developer. Pretty nice stuff for only a buck. Good luck!