Dee Dee, I had issues with this for a while, too. I actually just got a scale today and feel a lot better about what I'm feeding, but it's not completely impossible to gauge how much to feed without weighing them. Having a weight just makes me a feel a bit more confident.
I had the hardest time deciding if I should upgrade to fuzzies. When I finally did, it became clear I could have done it a long time ago. I read something that suggested to start with pinkies, and when they can take one very easily (they gobble it up without taking much time to loosen their jaw), move on to two pinkies. When they get to the point that they're gobbling those up really fast, as well, then move on to fuzzies (provided it's no more than 1.5 times the width of your corn, of course)
I started feeding mine fuzzies when he was about 1 1/2 feet long. It honestly sounds like it's time for fuzzies, but it certainly won't hurt to finish off your pinkies first. I would feed two pinkies at next feeding.
Try going to you tube and searching "corn snake eats fuzzies" if you're still not sure. (just try to avoid the live feeder videos if it bothers you like it does me!) I did that, and saw a snake that was obviously smaller than mine eat a fuzzie with no problem. Of course, I'm not saying trust everyone on youtube, but the video made it clear that a snake of that size could handle a fuzzie without any issue.
Also, after weighing my snake for the first time today, i realized according to the munson plan he could be on hoppers right now.