Asian-Trekking, SevenSummits Treks and Monterosa-Nepal are all KTM agencies that do north side BC-only services, though there are many others that can or will do it if they have the numbers, such as IceLand Trekking.
As for non-KTM companies, SummitClimb also do basic services or more assisted climbs, including fully guided. You need to do your research though and work out just what you'll be getting and what the contingency arrangements are e.g. what happens if you need to stay longer than the rest of the team? what are the rescue arrangements? etc
When you look into it, actually very few people have climbed the north ridge of Everest using BC-only services, with no Sherpa assistance, let alone no O2. Most fail, some die.
Otherwise Alpenglow, Project Himalaya, Kari Kobler, Adventure Peaks (UK) and others do guided climbs, at higher prices.