Secondary glazing or replacing with PVC patio doors?

[zo]

I have large aluminium framed double glazed sliding patio doors. They are quite old. The seal is fine between the glass panes. My problem is the area by the patio doors which is an extension leading to my through lounge gets very cold. Thus making my front room cold.
Replacing them with PVC new patio doors is very expensive as I would want good quality doors providing the best insulation.
My other option is to have secondary glazing - perhaps wooden frames with large sliding glass sheets. Will these be efficient and keep the area as warm as a PVC double glazed patio doors?
How much approx would it cost me?
Thank you.

 

[calorific]

Any chance of hinting at size?

TBH, by the time you've finished faffing around with secondary glazing (which will clearly reduce drafts and noise) then you'd probably have been wiser to go for the UPVC option anyway.

 

[zo]

The size of the Patio door - ht 204cm and width 240cm, not including the wooden frames.
Is there a real difference between aluminium frames and UPVC frames with regards to retaining heat?