No oranges yet?

I’d think I’d go for an extension if it’s within budget. As others have said, he orangery will get really hot and need blinds and roof blinds which will rapidly add up in cost. We’re having a roof lantern fitted in our extension and I contacted some lantern roof blinds companies yesterday to get rough quotes and for size of ~2.4x1.3 one company said between £1479 and £2233, and another (without size guide) said £2-5k You might need that regardless of the orangery vs extension debate of course, however presumably it’d be larger in an orangery. Plus all the blinds.

At least it’s all inches - we sometimes get a mix of inches and centimetres ( and evening millimetres too ) on some survey sheets we get back when we are designing with clients - we don’t mind as we can soon work it all out and check it adds up ! Lots of options for a space if this sort of size - if you want some ideas - click on my icon or name to have a look at some of the plans on our pro page, as a starting point !

Personally I think you should take out much of your current back wall and open the current living room up to the extension. Your plan makes the room that is currently best in the house and makes it windowless - I say make your best room better.