I like large anal toys too, but do you really mean it when you say "permanently opening myself up"??! If you did that you'd be incontinent - your ass stays shut normally for a good reason. Some people have actually torn their sphincter muscle and ended up this way so be careful and take it slow!
What you need to do is just slowly ease your way up in the size stakes, gently stretching your ass with larger toys so it becomes more flexible. I'm talking months here. What you'll find is that so long as you insert the largest size comfortable each day, you'll stay flexible and gradually be able to take bigger and bigger things naturally. You wont damage your intestines unless you use something too long. Dont insert more than 8 inches maximum, or less if it becomes uncomfortable. And take an enema before you insert anything as well.
I have a very good anal training kit I got from the US. It has six dilators in increasing sizes. When I first got it I could only take number three comfortably, and the larger ones looked HUGE to me. Now I can easily take them all and I'm even looking for something bigger so I guess it works! LoveHoney don't sell them so I'll email them and suggest it to them.
Oh yeah - I had an inflatable butt plug but a) the balloon burst and b) I dont rate them. The balloon inflates INSIDE your ass so your ring isn't stretched at all. Much better with a dilator / plug / dildo.