DIYer
this is what i do, and have done many times with wardrobes etc
what width is it, do you want a door the full height
you maybe able to get a standard internal door same as the one on left
and then infill the top, which can be wallpaper or painted to match room
Still have the height to the top, just add a shelf about 1/2 / 2/3rd in
can you still get the picture frame moulding to match and bring that round
a bit of an internal frame and architrave and normal hinges
Maybe a closer pictures of the existing frame