When double glazing becomes misty or full of condensation it is an indication that the seal between the glass has failed. A blown double glazed panel also won’t be as thermally efficient.
Below is an example of the improvement achieved by replacing a misty double glazed unit.
Double glazed units come in several thicknesses. This is set by the UPVC frame that you have. To increase the insulation of the glass you’ll be looking for coated glass and argon filled. Coated glass such as ‘Low E’ will have the benefit of being cooler in summer as it can reflect solar radiation.
Panels that are low to the floor will probably have to be BS or toughened glass. This is to protect children who may run into it and otherwise shatter the glass into dangerous shards.