I have office 365 also... I am on a Mac, a PC, and my iPhone. I have started using a combination of OneNote/Outlook for my GTD application. It's almost the same on all four platforms (web counts too) and can be set up just like a paper organizer.
I have a main notebook that has sections for COLLECTION, NEXT ACTIONS, CONTEXTS, PROJECTS, WAITING ON, and SOMEDAY/MAYBE. PROJECT SUPPORT and REFERENCE are separate Notebooks that I link to from within my main notebook.
I haven't exactly figured out the adding tasks and stuff from Outlook, but am working on it. At this point, it's just a matter of copy/paste as needed. OneNote does checklists, inserting of spreadsheets, PDFs, images, audio and video. And outlook is on both Mac and PC. I use the online version for the iPhone.
It actually beats all the other software and paper methods I've tried over the years.