Eclisse are able to supply bespoke sizes (up to 2m wide and 3m high), in addition to their standard sizes. Another company is Sugatsune.

Eclisse.co.uk make double telescopic pocket doors. I have a single frosted glass pocket door from them and I can confirm that it looks how I expected from the website. I'm not sure if they have a showroom.

Try here:- Sliding Door Stuff, I know they do extra tall doors, probably best calling them

I agree with 4 Panel sliding door cause it make it unified with the other windows on the left (each panel in similar width), For the front adding small porch with landing and gable roof Will make it more welcoming I just concerned about the half cladding at the front it gives of the vibes unfinished building, usually half cladding wrapped around all the second story exterior But from the front and back picture you share it seems the cladding of second story on front and back were different color so at least you should paint it the same color if adding cladding to the second story too expensive for temporary I would recommend move the tv so it didnt covering the window, if you add sliding wall in the wall section of the bottom right corner room and use Murphy/sofabed it can be used as guest room Change the orientation of the closet near enterance to get bigger foyer and space for small window to get more natural light Change the WC door opening location so ITS more private and open up the wall so the hall feel more spacious