Try practicing (without hoop) standing on the floor leaning over your bed. That way if you fall, you'll just land on the mattress. Where in MO are you?

The key to doing a backbend from standing for me was to make a frame with my hands above my head, and look through them to see the ceiling, the wall behind me, and then the floor. Before that I'd just been squeezing my eyes shut and hoping that I wouldn't fall on my head.... keeping my eyes open and spotting made it much less frightening!!

It might also help if you work on doing bridges. Where you sit no the floor and push yourself up into a back bend that way. You should have both hands on the ground so it won't work with a hoop. But when you get your back stretched out a little more it'll help with the actual back bend. Also bending over backwards onto say a counter with a pillow on it or something will show you what it feels like to bend back and once you get more comfortable you can choose lower surfaces. And that way you won't fall completely over because something will be behind you.

Thanks everyone, I think I'll work all of your suggestions into my practice.

If you can, make some videos of yourself doing this so that you can see the position of your arms/pelvis (as opposed to twisting your head around to see yourself in the mirror). Make sure that when your hands are on the floor, they are underneath your shoulders or a little further out. Similarly, make sure that your feet are underneath your knees or a little further out. Really think about pushing your pelvis forward, rather than trying to arch your lower back.

I recommend starting with bridge ups so that you can get good form in your backbend. Once you know that you're doing that well, try starting from a standing position. You need a lot of core strength when you start from a standing position, so take your time. Don't try to fling yourself backwards too quickly or you could end up hurting your wrists by putting weight on them too quickly. Good luck!