With your keyboard open in your messages app, click the small keyboard icon at the bottom right corner. When that opens, next to Samsung Keyboard click the gear icon. Find Style and Layout and open it. Turn on Keyboard Toolbar and exit.
Now on your keyboard Toolbar, you should see added to the ribbon a round-shaped smiley that will contain the standard icons, a square-shaped smiley with the lower corner peeling up that contains bit-moji's and stickers, and a square icon containing the word GIF.
That should give you more options than just the stickers in your messages.