Just done it the other way… A to H myself.
Did the ATPL-bridge course theory with Bristol, its only less than half the subjects (Category specific ones) needed than full 13/14 subjects. As I fly full time FW I went modular so did PPL course and checkride, followed by time building and now due to crediting of hours am finishing off my CPL(H) as you can start CPL course with less total time in the “new” category.
All theory gets covered by the ATPL stuff so just get stuck into the practical training.
But download the FCL as advised.. many of the credits/breaks you get converting from FW to RW and vice versa are listed there, but need to found as they are hidden in last sentences within paragraphs etc..