The ultimate thing to remember here is that an extension should be a balance between form and function. Here is a good reference site: https://www.conservatorypro.co.uk/glass-conservatory/
Detached Conservatories & Garden Roooms
What are my choices for a new conservatory design?
Pricing should only be done by a professional who comes to your home, completes a survey, discusses your preferences and budge then comes up with a written quote and you can get all that from https://www.localconservatoryprices.co.uk/conservatories/