I’ve been doing this for years – largely out of laziness, and not being arsed to change when I get to work, especially if I’m only going to be in the office for an hour or 2 before heading out to site. (and my steelies are heavy and less comfortable than my SPDs)
Any black/grey generic trainery type SPD works for me. Currently on Tevas, but have been through a few pairs of Shimanos, which generally seem to last longer than almost anything else.
Sole stiffness, or lack of it doesn’t really bother me. Comfy shoes are comfy shoes.
As above Quac Pham do some “traditional” looking stuff, and Giro do some fairly smart looking models too. If you’re near London, Condor generally have a decent selection of this kind of thing.