We can install a frameless 8mm hinged glass door inside your existing door so you don't need to replace it. Then, between the new inner door and the existing door you place any venetian of your choice. This photo is an example with shutter blinds inside a double glazed window by Euroglazing in Sydney. ...

Thanks for this suggestion. I need to be as snug as possible in the cold winter months here in Beechworth, ( the rest of the year is glorious), and I'm looking for the most effective insulation for the windows. I believed cellular blockouts would achieve this, but then thought Double glazing + blockout might be "over the top". I can't see draped curtains being so effective; perhaps I might settle for the blinds, and add some curtains for decorative effect. I can pay $3000.00 if they will achieve the insulation I need.

Put a rug under your work area and hang some heavy curtains would be cheaper. But all 3 better

I'm with your hubby I'm afraid. Double glazing is mostly a way to deal with cold radiating into a house, and heat leaking out of the house via conduction which is not the problem in Perth. Sure it will prevent heat from radiating into the house via the windows but mostly that's not how houses heat up in Australia. What causes a house to heat up is sunlight warming up the ambient air inside the house via a greenhouse effect which double glazing will not prevent, or hot air being born into the house on the wind. So double glazing will only prevent this if you intend to shut the house up all day. In which cause it's just the lack of air movement not the insulative properties of double glazing doing that. Single glazing would also do that. In Australia what matters most is cross ventilation in order to create a restful environment. Evaporative cooling works effectively when you have good cross ventilation as it's the evaporation of the water vapour causing the cooling effect. Additionally you do not want to shut up a house with evaporative cooling as you'll get condensation and mould inside the house. So if you are 100% on double glazing it will only be effective with refrigerated air conditioning as it's relying on preventing air exchange between the inside and outside of the house to work and preventing conduction of ambient air temps. Double glazing is not popular here for a reason, it's the wrong solution for our climate. Cross ventilation and proper solar management is the correct solution for our climate. So I'm with your hubby I think it's wasted money that would be better spent on controlling the direct sunlight to the home and proper ventilation.