If you find the AutoThrust is "lazy" on an approach you will probably find that the conditions are smooth and your sidestick inputs are also "slow" and smooth.
To "wake" the AutoThrust up and have it respond quickly, simple make some rapid (tiny) sidestick pitch inputs.
The way it was explained to me was that rapid sidestick pitch inputs cause a phase/gain shift in the AutoThrust response. This in turn makes thrust change response time quicker and magnitude larger.
Don't be over-smooth, fly it like a Navy carrier approach, hold the glide slope as accurately as possible with lots of tiny and timely sidestick pitch inputs.
You'll have that sucker eating out of your hand in no time!