Hi Mich,
We recently started looking at this at work. The current recommendations are light exercise as tolerated.
What I used to tell my patients was to listen to your body. If you feel tired, have a rest. If you have some energy, use it and take a light walk. I also used to tell them to try and get up every day and have a shower and get dressed. There may be some days when after this you may want to go straight back to bed, but other times when you do that that you feel so much better. Activity creates energy and the less you do, the harder it is to get going again. Getting a decent nights sleep and a good diet helps too.
Now of course this is all a nursey point of view, let's see how I go with my own advice once my own treatment starts!!!!