I suggest you contact Alex at Bristol Ground School for advice.
I am not sure, but I think you need 150 hours to commence your CPL flight training. So best to time your finishing your ATPLs at a time when you have 150 hours total time. I would see how many hours a month your doing and then work out how many in 2 years you will do, minus that from 150 and then start your ATPLs correspondence course when you get to that flight time.
Where do you live ?