I took the same approach as you initially by doing one bedroom in order to test viability. I used a single DRB module in place of the light switch and a LTH module in the ceiling. I then later added a DRH module at socket level to control an electric heater. I have a small 1.5c offset on the LTH which I found works well although if your heater/radiator is directly beneath then this will be less than an ideal situation. With underfloor heating I don't foresee you having any problems. Personally I am more interested in getting a useable proxy reading than a totally accurate measurement.
It is also useful to remember that there are a lot of factors besides temperature that influence comfort levels so yet another reason why I feel a useful proxy is more important than getting too hung up on accuracy.
In my most recently altered bedroom I opted for a DFP panel which is at shoulder height in place of the light switch which gives a more accurate and useable reading. Now I am sure that the Idratek system is useable by the rest of the household and visitors I am less inclined to stick with "traditional" light switch locations and I am considering moving this to above a bedside cabinet.
There is an interesting discussion on black bulb sensing here which may also be of interest http://www.automatedhome.co.uk/vbull...ead.php?t=2203
I am using a DFP in my bathroom which is within regulations however you should note that switching of any LV (Not ELV) should be done elsewhere.
Perhaps ceiling mounting would be the best option for other modules?
Yes thats right.