Hey,
Yes i do recommend using a textbook for bus man. even tho textbooks may not cover all information or sometimes include unnecessary info u dont need to really know, some of the case studies and real life examples it provides can be quite valuable as you can use them in your answers and shine out from your peers. Also bus man is a subject where you might benefit from that extra background knowledge (and most textbooks provide that), so it is always a good idea to look through the textbook ( as well as other mediums i.e. the newspaper) for some real life recent examples of concepts, etc. but in terms of notes, dont jus rely on a plus notes or notes from other companies, because u learn and consolidate more info when u write notes urself, but do surely use other people's notes as a guide to your own notes. And dont simply copy their notes, summarise into a way that you will easily understand when it comes to sac/exam revision.
hope it helps. Wishing you all the best for your bus man studies