For the theory, I recommend CATS. They teach both A and H so they know how you work already, and how best to get you through what you need.
For the flight training, recommendations depend on where you are based. I have personal experience of both Central Flight Training (Tatenhill) and Command Pilot Training (Coventry). Both are advanced flight training schools with lots of experience in dealing with bespoke situations such as yourself. They can also recommend the best place for you to do your PPL(A) with your planned conversion in mind. You could do worse than Leicester for your PPL(A).
These recommendations are Midlands focussed, with the exception of the ground school. I am sure that there are other equally good schools elsewhere, which might suit you better if these aren't geographically convenient.
Good luck!