Well you can go round the houses with free and subscription sites but the information you glean will mostly have no guide to accuracy.
The exception is the CWGC
CWGC - Casualty Details
For the small fee of £3.30 you can download the Summary of Events section of the Operations Record Book for No.75 Squadron (unit given by free CWGC site) and get it from the horses mouth.
Squadron Number: 75 Summary of Events: Y | The National Archives
The ORB also lists previous operations he took part in for the month. This will not be available from any other web source.
This will give your research a stable footing for looking at other sources eg W R Chorley Bomber Command Losses, 1943.
Regards
Ross