Yes, being able to control the heat pad is very important. I'm not sure what is available on the European market. I would suggest sending a PM to Dr. Del. He is one of the Admins on this forum and lives in the UK. He may be able to give you some suggestions for thermostats.
Also I suggest only using no more than 1 inch of substrate. This will let more heat through and should give you warmer temps on top of the substrate...