For wearing around the office, I’d say a good flannel suit is worth looking into. The grey flannel suit is somewhat of a long-time staple piece of a man’s wardrobe before modern HVAC systems were introduced to most workplaces.
For a more casual alternative, I think a tweed suit might be worth tracking down. The instances when you can wear a full-on tweed suit though might be sort of rare. I wouldn’t consider it office attire, given that tweed’s origins were meant for it to be worn in the countryside, not the city.
Still, I like tweed suits because you can break them up and wear the jacket and trousers separately with other elements of your wardrobe, which is what I do quite often. I was lucky to find two of mine at thrift stores (both donegal tweed).
As for where to buy new, that really depends on your budget. Be warned though that finding either types of suiting isn’t going to be something you can find on the cheap. Lands’ End has a flannel suit that’s gotten some mixed reviews in terms of the quality of the flannel used. The only tweed suit I’ve seen from memory would be from either J.Crew or GANT by Michael Bastian.