If those boxes dont work very well, we can design our own boxes or look for another ones. That is not a big problem.
Either way, I would probably have the same problem with IR sensors with any boxes I use

 

If the target where the information will be sent is ARM (Atmel 328) or any other computer, then NIMO TSYS 02 would be ideal candidate, cheap, sensible until last two digits even at meter distance and all circuit is 4 wires to ARM. Namely "digital 16 bit thermometer". There exists even the 24 bit successor model 01, but that is overkilling.