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There's a dedicated thread on the M2 forum detailing what many did for sound insulation but lots of the methods involved restoring the deleted insulation pieces from the regular 2 series, so that wouldn't apply in your case.
If you do some search online, there's an extensive test data regarding different brands of CLD tiles.
General consensus is the butyl-based deadeners are more effective than asphalt-based products.
I have applied Dynamat on metal surfaces prone to resonating and then applied the acoustic foam on top.
Acoustic foam work as sound absorbing/decoupling barrier vs. the CLD tiles working as sound deadening material, so installing both on applicable surface will increase the effectiveness of sound insulation.
I did not do the floor as it involved extensive removal/reinstallation of interior parts, but just doing them on the door, rear cabin and trunk area made a huge difference.
Eliminating rattles while doing so by applying butyl tapes on the suspect area helped a lot too.
Obviously the M240i has more sound insulation material than the M2, so YMMV.
Hope this helps!
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