I wouldn't worry about gear if I were you. The quest rewards are decent enough to keep you moving to a point where what you have will serve well until it is replaced. Being that close to 60 just wait until you hit Outlands. I am on my first quest to 70 (currently 67 and so close to flight form I can taste it) and I was surprised that what everyone said was true, your first green item in Outlands will dominate any epic you got pre-BC (If you've been through Outlands you know this already, but I was very pleasantly surprised.)
Anyway, at 40 you should have enough quest gear to move you along without issue. I did most of my questing solo and a little bit with a friend or two, I didn't die very often (unless ganked) and went through 40s pretty quick.
Though I know plenty of people that have and do worry about gear, my thoughts have always been if I am questing enough then I will outgrow my gear on it's own so why spend $$$ on gear. I guess instances can give XP, though it is usually shared and will a full group pretty low and there can be excess waiting to organize time associated with them so just quest on and you'll be fine.