TBH the Telestart is all you need, I can start mine up to 1000m away and by the time I have walked to the van it is more than warm enough. Thermocall is a bit over the top if all you need is to switch on from the house which is adequately covered by using Telestart or a timer.
Telestart HTM100 which is the 1000m range is just over £420 list price UK but can be purchased for around £270 from Germany. ( That is what I fitted to mine) Easy enough to fit yourself, you don't need an installer. No sim card worries then.
Thermocall is around the same £400 price, maybe a fraction cheaper. Install yourself again.
Depends upon what heater you have fitted as to what you can use as I said earlier.