Conservatory between two existing extensions?

[YodhrinForge]

I have this odd little space on my property around the back between my neighbour's existing extension(built up to the property line, so is a party wall) and my own house's existing extension. It serves no real purpose, it's north facing and the ground level is shaded by the extensions so nothing useful will grow there, it's inconvenient to use as a bin store, and it features the downstairs bedroom's only window so regs won't permit a "proper" extension there, it's just generally dead space. My only initial idea was to stick a couple of sheffield stands around there in case any visitors come by bike, but sitting in my little back porch the other evening which unfortunately will be getting demolished to make way for a utility room(and moving that isn't an option since it needs to be in that spot for various reasons) I found I actually quite enjoyed having a sheltered wee space to read and listen to the rain hitting the roof looking out to the garden. The space is about 2.5m wide x 3.6m deep and apart from having to faff with the drainage and guttering(which all needs to be addressed as part of the broader renovation work anyway) it *seems* like it would be a fairly simple extra project since it would only need the roof and frontage, but from attempts to research it I'm finding the "conservatory industry" seems pretty thoroughly geared around a few standard designs all of which are intended to project outwards from a wall rather than be fitted between two existing ones, so I take it I'd be looking at a custom design? Does anyone have experience with rough costs for that sort of thing? Would it be easier to go to a specialist company or could I be better off just getting my existing architect and structural engineer to specify it and order individual components myself? Given I'm in the central belt of scotland and it's north facing it'll have to be triple glazing so that narrows my options.