You don't officially need 'A' Levels but it's great you want to take them! Biology for sure, but the other 2/3, up to you! Psychology might help! There are 'Paramedic Science' courses at Uni but they're not necessary.
To be a paramedic you start as an ambulance technician which is a 12 week course, in which you only need GCSE's and some healthcare experience - it might be worth seeking that in a hospital or nursing home? Then you gradually progress on until you're a paramedic.
Also you need to be physically fit and to have held a driving licence for at least 2 years!
Good Luck! :D