If you really want to drop out of A levels then fine, do it. But do you have set in stone plans for what you're going to do? What job are going to get? What job will take you on with just GCSEs? Do you have any work experience, any reason why a job would take you on when there are so many more applicants who have A levels and more applying?
I'm not trying to discourage you. But you need to think this through very carefully before you quit. Quitting is easy by the way, I did it myself and I just had to go to the office and ask for a form. They send you to a few people to "chat" about it but if you fill in the form you're done. What you do after quitting is the hard part. I've spent the last two years looking for a job with no luck at all.
Can you write out a plan of exactly what you're going to do once you've quit? Write down: Who you are going to apply for jobs with (you'll be applying to several people). Make sure you have an up to date, well written CV, and are ready to go to numerous interviews. Write down what you will do if you don't find a job. Will your mum be ok with you hanging around doing nothing? Will you go and get a volunteer job (looks good as experience)?
You say you want to get a studio flat, ok, well do you have any savings? Work that out, work out the costs and all that. You'll probably have to be working for quite a while before you have the stability to rent anywhere. It's not cheap, but there are lots of threads in the Money section with living cost estimates you can check out.
Before doing ANYTHING, make sure it's all planned out. Otherwise you could drop out and end up sitting around doing nothing. That is not good. If you have a depressed mindset already then this will be very hard. Motivation when you are depressed is nearly non-existant. But if you can do it, then great. Just make sure you have all eventualities planned out. It will NOT be easy. But good luck with it if you do!