Sorry, just stumbled across this and thought we'd chip in - in case anybody else came across it. There are load of good 3 and 4 bar options with different profiles: heritage internal doors We'd be intrigued to know/see what you ended up going for? And how you feel about it now?

The thermal qualities of new ones would be preferable. When I had new patio doors (sliding) I couldn’t believe how much cosier the room is now compared to the old 1980s one. Your examples are beautiful. I recently had one of the large double glazed panes changed to accommodate a cat flap (safety glass cannot be cut) and I was quoted £370 - £650 for one pane. I chose the cheaper quote but just to let you know of possible costs to change the glass.

It sounds like you’re making great progress with your home's updates! If you're looking to create more space in the garden, installing sliding patio doors in the dining room is a good idea. Sliding doors allow for a more seamless flow between indoor and outdoor areas, especially in a smaller space like your courtyard. As for security concerns, modern sliding patio doors have improved greatly in terms of safety. While older models might have been prone to being lifted out of their tracks, today’s doors have advanced locking mechanisms, reinforced frames, and anti-lift features that significantly reduce this risk. Many manufacturers also offer options that include internal security bolts or multi-point locking systems for added peace of mind. If you’re worried about security, you might also consider adding domestic gates or additional fencing around your courtyard to reinforce the area further. That way, you can keep your home looking open and inviting while still maintaining privacy and protection. Ultimately, it’s about balancing aesthetics with security, and from what you’ve described, sliding doors could be a great fit!

Above a room with sliding door