Latex levelling compound with UFH

Hi,
Not sure if anyone can advise on this. I have underfloor heating installed with a concrete poured floor. Now I'm looking to build up the floors by approx 6mm to avoid having to use saddleboards between rooms that join with a semi-solid wooden floor. I was going to use just a normal water based self levelling compound to do this but in the last few days people have been saying to me to use a latex based one because of the the UFH needs a flexible base. I know about having to use flexible adhesive, grout and glue but this is the first i've heard of flexible floor compound. The latex one is a good bit dearer and the builder is now going mad over having to use it and wants to use the water based one. Has anyone come across this before or is this just overkill and also does the same apply for tiles and semi solid floors?
Thanks!

That could be a very expensive way to avid using saddleboards. We had underfloor heating, and yes, the tiler insisted on using latex leveling compound. The builder agreed with him.

I can't remember how far a bag of leveling compound does, but it ain't much..

Thanks for that, it confirms what we thought. Its not just for the saddleboards sake but we have some tiles meeting the wooden floors in an open area plus the builder didn't leave the floors very level or smooth to start with so he knows its his fault and is just going mad now at having to do this now. The cost is about double for the latex verus the water based (13 euro and 25 euro a bag) but about half the house may have to be done now to get the floors good enough to tile.