For average shooting under average conditions, the system you are using will work. Use it now while you are getting your feet wet. You'll do all right.
However, as you learn more, you will likely start to shoot more and more "non-average" shots under "non-average" conditions. Your in-camera meter will become less useful to you.
You will eventually want to get a regular exposure meter and learn how to use it.
Keep doing as you have been but start hunting around on eBay and in the classified forums. When you've found the thing you want and have saved up enough to afford it, buy.
Even if you don't use it right away, you'll have it when you need it and you can take your time studying and experimenting until you get the hang of using it.