Unacceptable! Mixing should never take time!!!
I'm really impressed by what you were able to do with nothing! You accomplish so much more than many people on this forum with thousands of dollars worth of gear!
You're not going to be doing any tracking, are you? If you aren't, then your options for headphones explodes, because the requirement of sound-isolation is much lower than if you were! But...
dxavier has a point. I don't like to gush, but you're quite good, and I'm impressed by your signature. What do you hope to gain by buying equipment? Without a clear set of goals, you're throwing yourself into the gear-spiral, because unless you have oodles of cash (which you don't), there's ALWAYS something "objectively" better!
Don't listen to anyone who tries to tell you what you want.
Of course, I'm going to be a minor hypocrite and say that as far as headphones go, you should upgrade. :P As long as you know what you're looking for. If you're not tracking, I recommend sticking your nose in some semi-open or open cans; unlike closed headphones, people somehow make an argument for them when it comes to mixing.