Don't worry about taking more GCSEs, except as Nicoley-oley says, the maths which you will probably need. Universities don't usually pay too much attention to them for mature students. For social work, an access course with psychology and sociology will probably be most useful to you. If you know which university you want to go to, drop the admissions tutor an email to ask their opinion on which access course they would prefer, including as much detail about the modules as you can get.
From what you've written above, it's clear that you can express yourself well, which is more than half the battle: you will do fine on Access if you are committed to it.