Yes I am now using a thermostat with the UTH.
I realise where the holes were in my understanding.. I did not know the best way to position the thermometer/sensors etc, and could not get accurate readings.
The heat spot is now consistently between 34-35 degrees celsius.
I am pleased to say that Amadeus is much more himself again. After a few quiet days, he is more relaxed and moving around tonight. When I positioned the sensors, I had to hold him briefly to move him, and he felt alot better and stronger, his tail curling around my hand as normal.
I will see how he gets on in the coming days.