Thanks, Waveylines - my problem is that being in bed gives a falsely warm temperature, because I have had to adjust the bedclothes to get warm. As this is not a calibrated science, I can often end up a wee bit warm, which would give an elevated temperature if I stay in bed, but that is better than too cold for sleep. Book also says not wear bed socks - I need bed socks to keep my feet warm, and to stop them waking me when I subconsciously move them to another part of the bed. Even during the day I am adjusting to keep warm - and if temp is such that a top is slightly too warm, that may be better than too cold.
How does basal temperature work when I need to physically adjust clothing, and can over compensate? It is a bit of a mystery to me - and it is supposed to be a real help to monitor progress.