Get EASA Professional Studies by Phil Croucher. All the ATPL syllabus in one book straight to the point. It's my main source of studying. If you want an "app" then I am happy with Bristol GS, but get that book anyway.
Because of the nature of the EASA exams, you do need a good question bank and if you are doing your exams at a UK CAA venue then you should be good to go with Bristol GS question bank. If you are doing it under another CAA then Aviation Exam has more questions. Bristol GS weeds out questions that they know are not asked anymore by the UK CAA.
And if I am not mistaken, given your situation you don't need to be enrolled in any ground school course and you can do everything at your own leisure.