rederikus gave a pretty clear explanation.
The short answer is that 1000mA and 1500mA transformers should work fine, as long as the voltage is rated 24V AC (or anywhere between 22V to 29V AC).
It’s a common misconception that higher current rating will damage the circuit — the current rating only indicates the maximum output current (i.e. how much current the transformer is capable of delivering while maintaining the rated voltage). The actual current depends on how much the circuit needs.