self study
self study is the way to go.
if you are only just starting your flying training you have plenty of time.
If you start studying now, aim for about 1 subject every 4-6 weeks you will have enough time before your CPL flight test to nail your KDR's.
I used BT for all my CPL including IREX and passed everything 1st time with great results.
For your ATPL's go for AFT in MCY. Im halfway through and finding AFT very good indeed.
Don't rush your study, spend the time and aim for more than just a pass.