Here are a few examples of 2.5 D animation technique that would work really well in the proposed style.
The animation elements are designed and then placed into the 3D environment on top of the live action. The great thing about this approach is that the lighting and mood can be manipulated in any way which means that the visuals can have endless looks & feels.
The examples below are all so different in terms of visual style however the same technique has been applied.
This is a perfect way to bring the creative to life and create a seamless and premium finish.