a good upvc branded window with trickle vents a 24mm or 28mm Double glazed unit and a multichambered frame (maybe with the new thermal inserts) will definately reduce heat loss through the window and reduce condensation - it will look better too
security is no problem - go with someone who...
i have synseal windows and patio doors in two different houses and they are great. one is an ultra modern flat development with gray foiled windows on the outside and a naural pine effect on the inside.
the othe house has their lead free vertical sliding windows in and they are a huge...