We had a similar dilemma (with a mid terrace), and as nice as Crittall look, we decided to go for two tall tilt and turn windows and a set of French doors in the middle of the windows. It’ll always be a matter of preference, but we decided on this configuration as the extension is the only entrance to the garden and having the flexibility to open windows for ventilation and a door to access the garden made sense to us. Good luck with your decision.

Rather than having a door and glass panel made to the exact size it would be more cost effective to put in a standard sized door in a new stud wall. There are lots of wood doors that are glazed and have the look of a virtual steel door but at a lower price point: https://www.doorsuperstore.co.uk/product/jb-kind-urban-industrial-internal-clear-glazed-metro-black-door-762mm.html?msclkid=594310d076641559e1e47038523a526d&utm_source=bing&utm_medium=cpc&utm_campaign=SCT - Catch All Low Bid PLA&utm_term=4576511000066512&utm_content=All Products PLA#images-6 Bare in mind it will always have doggy nose prints on it. Also don’t forget this type of door will need an extra long door latch (so that the handle is in the intended place and not weirdly close to the edge) so make sure you use a really good joiner to put the door in.

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 doors that you are considering are most attractive and I love the reeded glass. Biggest question who is going to install them? If you are doing it yourselves then measure the existing opening at least 3 times very accurately. If they don't fit you will be wasting your money. Just a small point. Your architrave is quite fussy for the clean lines of the proposed doors so consider replacing that with something simpler at the same time for a better result. Research the supplier as thoroughly as possible. Read all the reviews especially regarding the quality and the ease of return if they are not suitable. Do they come with fitting instructions? Is there any guarantee?