"js.b1" gurgled happily, sounding much like they were
saying:

Mirror reflective metal venetian blinds? Venetian blinds can then be
wound back up when not needed, only needed a few weeks a year.

Not an option. There's vertical blinds at the mo - and we've already
tried to get those replaced for purely functional reasons...

Then you need to sort out a few extractors - window mount Ventaxia or
Xpelair 12", get a good cross-flow of air moving which will greatly
reduce perceived temperature re discomfort.

Unfortunately, definitely no chance of it being an option...