Dizzy, not really. Only electric blankets cause a significant change in body temp. Here's what FF says:
What factors influence my basal body temperature (BBT)?
'There are certain factors that can influence your basal body temperature. These should be noted in the notes section of Fertility Friend or checked on the checklist/specifics on the data entry page.
These factors will usually not make charting and chart analysis impossible, especially if they occur only rarely, though it may be more challenging. In most cases, even when these factors apply on an ongoing basis, they will not skew your data so much that reading the chart is impossible. It is important to make a note of the factors, however to help with the interpretation of the chart. The following factors may influence your BBT:
fever
illness and infections (even those that do not produce a fever)
cold, sore throat
drugs and medications
alcohol (especially in large quantities, though all alcohol consumption should be recorded)
smoking (if you smoke, you should consider quitting before you are even pregnant)
emotional stress
physical stress
excitement
sleep disturbances (insomnia, night-waking, upsetting dreams, poor sleep)
change in waking time
jet lag
travel
change of climate
use of electric blanket
change of room temperature
recently discontinuing birth control pills
breastfeeding'