Hi Lucy,
I had the privilege of studying under Karen Wallman (University of Western Australia) who has a special interest in exercise for CFS. Here's one of her articles :https://www.mja.com.au/public/issues...al10079_fm.pdf
She's published a lot of articles on the topic so if you search under her name, I'm sure you will find some good information.
Because I have had that background, I do feel pretty comfortable with dealing with CFS patients and prescribing exercise programs. In my experience, as long as you start very conservatively, the results are positive and the patients can see the value in what they are do (in terms of objective and subjective outcomes). When I have done brief literature searches, the prinicples which stand out to me is that aerobic exercise is the key priority to increase endurance with ADLs (however resistance ex are useful and can be included). I also am aware of pacing principles and find it important to discuss with patients that they need to be very consistent with ex, even on not so good days (and not do any more than usual on good days). I use small progressions and teach them about how to progress independently.