Nikkor 90mm f/8 or f/4.5 if you want/need a bit more light to see/focus indoors, Schneider 90mm f/5.6 XL if you want the "best" option with big IC and big aperture.

But, note that the filter sizes go from 67mm, to 82mm, up to 95mm for those lenses in turn, so budget accordingly if you need filters.

I used a Nikkor 90mm f/8 a lot inside an abandoned mill some years ago. In that situation it was definitely a challenge to compose/focus due to extreme darkness, and even f/4.5 would've probably been difficult. So consider your location as well. Some examples:





A Nikkor 120mm f/8 would be a great option for a slightly longer lens. You mention "stretching." Consider that the wide-angle perspective distortion is mostly caused by things near the camera in the corners, and your tastes may vary depending on the architecture in question. IMO anything longer would be hard to use indoors.

For me, I also liked to exaggerate the space with super-wides. As Jac mentions above, a 47mm XL would work on 4x5 and can get a unique perspective. The below image was with a 47mm but I don't see any objectionable "stretching," because I was not near anything to show that effect.



And if you fancy something in-between that wide and 90mm, the Schneider 72mm XL would be a great option with the same caveat of large filters (95mm).