Go with a combination of the two.
Get yourself a paper season ticket between your local National Rail station to a London Terminal (depends where you live; Paddington, Victoria, Euston, Kings X, Liverpool St to name a few). That then takes care of your National Rail travel.
You then apply for an 18+ Student Oyster card on the TFL website. Its £10 but once you have one, you can load a Z1-6 Travelcard onto it at with a 33% reduction compared to an regular Oyster card. In fact, depending on where your Uni is located, you might get away with a zone 1-2 Travelcard which is less than £20 a week for 18+ or just under £30 for regular travelcards. I think you would be entitled to one seeing as you are studying in London. Either way, all Travelcards are valid on any London bus in any zone, regardless of zone on your Travelcard.