>>Many have recomended to use resistors but is there any way to get muct better reading as resistors will change when it is subjected to heat.

What do you think will happen to your Power Supply +5v line when you subject it to heat?

Resistors come in all shapes and sizes down to 0.01% tollerance (or better). If you really want to go mad, try TANTALUM RESISTORS... that's assuming you can afford the price tag of several Dollars EACH (yes a whole heap of those green crinkly drinking vouchers PER Resistor!!).