??What the coolant also replaced back in 2015? In any case, you can buy just the water pump and replace just the water pump, but if you do that, you will still need to take things apart about in about 40k miles when the next TB is due. If it was me, I would buy the Aisin kit and some new coolant and do it all at once.
His timing belt is due in 2022 - every 7 years.