If I recall the CX flights arrive at FRA T2 where the BA flights also leave from. If you can get your luggage checked all the way through then you should be okay with 1:25h transfer time.

T2 is much easier to handle at that time than T1. Just be aware that BA has additional security screening before its T2 departure gates air-side, in a morning that can be a busy place to be.

If you cannot check your bags all the way to LHR then you will need to allow yourself a minimum of 40 mins from claiming your bags to getting on BA metal.