You will need to get qualified teacher status - you could train as a primary school teacher first and then move into special needs education. There are also degrees in special needs but they don't all have qualified teacher status - you would need to go on and do a postgrad teacher training course somewhere.
To get onto a teacher training degree you will need GCSEs in maths science and english (and I think you have to take a test as well) and usually 3 A-levels, (or other level 3 qualifications). You usually have to have done some sort of observation in classrooms. Rather than trying to take extra courses now, is there somewhere you could volunteer to work with younger children - e.g. at scouts or brownies. This would give you good experience to write about on your personal statement.
You can look for courses on the UCAS website.