Well, Paws, you've got yourself caught in a yucky perfectionism thing. Don't worry, you're not alone- leanonme already chimed in saying she totally relates. And the two of you aren't alone at all! There are piles of people who get stuck in this kind of thing.
Having to know everything, before it even happens. Having to know exactly what will happen as a result of ANY action we take. Having to be in control of any possible thing that occurs as a result of ANY thing we do... all these are the epitome of yucky perfectionistic thinking and believing.
It's such a miserable trap- because there's no way for any human to know exactly what will happen every single moment. But somehow, perfectionism demands that "if you're doing things right" you'll be "smart enough, clever enough, skinny enough, strong enough, funny enough, creative enough... (get the idea...)" to know everything that's going to happen, and to be able to control it.
Of course, since no human can be that all-knowing and all-powerful/all-controlling, and since perfectionism offers only 2 choices: be perfect or be nothing- you're stuck having to do nothing. This accounts for why making even a tiny change can seem so daunting.
Say you want to try eating one grape. You know that one grape has almost no calories, it couldn't possibly make you "fat" right? You know that intellectually. But then the perfectionism kicks in (and it isn't a rational process). And it says things like: "Don't do it. Don't eat that 1 grape. Chaos will ensue. You'll be out of control and won't be able to rein it in. It will be all your fault because you could have prevented the chaos by just not eating the grape."
And the perfectionistic voice (which is totally related to fear) is awfully loud. Awfully, awfully loud... And it frequently "wins' the debate. And... no grape.
The antidote, as leanoneme suggests, is to try teeny, tiny changes- knowing you'll have to go up against that perfectionistic voice. And then, when you've tried a teeny, tiny change, you need to pay careful attention to what actually does happen.
The truth is: 1 grape will do nothing bad to you. It will give you a few vitamins and minerals- and who can argue with that?! It will not make you "fat" or cause ANY kind of chaos. It won't alter the world on its axis, or create a tsunami or tornado.
When you do these "tries of teeny tiny changes" you really have have to "log" the results of your experiment. The perfectionistic voice will "try" to make you forget the results (the positive outcomes) and forget that everything turned out ok.
Going up against a loud, forceful perfectionistic voice is SO not fun. And it's so not easy. It is, however, doable. Much easier to do with pals around though, so as usual, it's good to be in touch with support people :)