If you do decide a degree is the right option for you, keep in mind you can apply for a student loan to cover the cost of open university degrees, if you've never had one before, which it sounds like you wouldn't have.
I paid for my OU degree with a student loan. It covered all the course fees, and they provided all the materials and books and stuff. They also have other support for low earners, parents, etc too. So worth considering if you do want to go down the university road.
I agree with a PP though, it's a lot of hard work to do, it's worth doing if you're looking to go into a role which requires a degree, and can open a lot of doors, but choose wisely, and be sure that you really do need a degree for what you want to do. Otherwise there are lots of other educational options. As well as Open Learn which is the OU free course section, you could look at Coursera.com which has a bunch of free courses and tasters on it, to give you an idea of things you might enjoy. Most industries have industry specific qualifications too, would your employer consider sponsoring you to do something to advance your skills?
Just for perspective, I started out doing admin, then call centre type customer service, went on to account management, some sales, and now work in software, as a kind of client liaison role for new clients getting set up with our software products. I got this job because I understood from my customer service background what the client's customers want, having worked in the same industry. I've moved job a bit to increase pay, change roles, and to move away from poor employers, by far my biggest pay jumps have been from moving rather than internal promotions or payrises.
Good luck OP, the fact that you're thinking about this is a good start!