We tended to use the card thermometers that came free with the grobags - really basic but a useful indicator with no batteries or electric to worry about. To be honest you can spend ages worrying about room temperatures but with central heating you probably have the house around 19-20 which is fine for you and baby. The card thermometers also have a useful temp guide as to which tog to use for which temperature range, or how many blankets/sheets to use.
The egg is a nice idea but ask yourself do you intend to stay in his/her room all night watching the colours and numbers change ?
The hardest thing is in the summer when temps get up and beyond to the 30's, do you use a fan to keep them cool or will that give them a chill, will the mossies get in if the windows are open etc etc - great fun
