Replacement for UPVC/Glass Conservatory

Hi all. We have a south facing house which currently has a UPVC and double glazed conservatory with a glass roof. It is virtually unusable in summer and freezing in winter. It is a reasonably large structure at over 5mx3.5m

We wondered whether there is any way of removing it and replacing it with a lighter weight but more insulated structure with a covered roof based on the existing dwarf walls?

I'm sure the foundation depth will be an issue but wondered whether as it suppots a glass roof at the moment there could be something out there that would not be much heavier all round maybe in aluminium or wood with less glass.

Any thoughts much appreciated.

You could just replace the glass with a better higher performance sealed unit:-

http://www.k2conservatories.co.uk/k2-glass/celsius-range/celsius-plus

Fairly easy to do and quick, your main outlay will be the purchase of the units, any where from £90 to £150 a metre trade plus fitting.