Here is an easy way to change things up and stimulate your baby. Take a small ball, not too small that it is a choking hazard, but not too large where it cannot fit into a plastic bowl. Roll the ball around the bowl so that your baby can see it. He will enjoy the movement as well as the sound of the ball.
If you have them, try balls made of different material. Explore the different sounds of a rubber ball, a plastic ball, and perhaps a ball with a bell inside.
And do not have all the fun yourself! Allow your baby to check out the ball in the bowl too. Prop him up on the floor and let him touch and enjoy. So easy, so inexpensive, and so stimulating!