Choose a transformer with secondary rating as follow: voltage ≈8-10V ac @ 500mA.
Bigger transformer, if physical size is not an issue, wouldn't heart, and it will not overheat because you don't draw rated current; it is opposite way around - if you select transformer with to small VA rating it will overheat.
Also to help you to select transformer-rectifier configuration, attached you will find "rectifier relationships" ..
Regards,
IanP