What levelling compound over underfloor heating?

Hi,

I'm currently refitting a first floor bathroom. The existing floor is chipboard - I am overlaying this with aquapanel.
On top of that I am fitting an electric underfloor heating mat - I've done this before and found it a pain to tile over afterwards due to the cables, so was thinking of using a levelling compound to create a smooth surface and make it easier to tile.
Could you please advise what type of floor levelling compound I should be using in this instance? Tiles going on the top will be travertine if that makes any difference.

Thanks