In my opinion I don't think you should be wasting your time with a university style degree as such - unless you do a specific vocational degree, such as medicine. I wouldn't do an airline management degree either, if you want a backup plan then I would stay clear of anything aviation related.
If you want a solid back up plan which could help in the future for a managerial role then I would look into accountancy. Without a degree you need to start one step lower than graduates but if you have an interested in the subject then its probably an OK way to start. Do an AAT (accounting technician qualification, I think). Unlike the more advanced accountancy qualifications I don't think you need work experience in an accountancy practice so you can do it via distance learning in your own time...which probably suits you if you already have a full time job in a different sector. If, for whatever reason, you leave aviation then you would be able to start at an accountancy practice without the need for a degree and become qualified as a chartered accountant...and from there you pretty much have a job for life and a guaranteed salary thats pretty good. If you decide to move into a managerial role in the airline, then having an accountancy qualification definitely won't impede you although maybe if you had real life accountancy experience it would probably help even more.
Either way I think its wise to focus on practical/vocational qualifications.