From my experience and imo the best security substrate is the Eco-earth which comes loose in a bag. They love to push it around and surround themselves with it. They will also push it in front of their hides. There are no mites to worry about. But the negative thing about Eco-earth is it tends to be kind of clingy to water bowls and hides and they can get a mouth full of it if they miss on a strike. That last thing is the reason I went to using Aspen. But I also hated the clingy-mess of Eco-earth.
I don't know if I would choose a substrate just for it's security use, the better idea is putting things in that make for security I like using fake plants like the kinds I bought at Family Dollar (see my gallery) or that are at pet stores. Hides which are fairly snug, etc. (if your hides are a bit large, Eco-earth does help make up for that I will admit.) But anyway I think keeping your ambient temps nice and warm 82-85 are more important and often overlooked. And not over disturbing the snake. Your right, using F/T is so much more convenient and a lot safer as well, but alas some never do go for or accept F/T and they become very proficient at killing their meal. That is why the younger they get on F/T the better and the more likely they are to switch. I would do the following things to help your switch go well.
1. make sure the feeder is thoroughly thawed and nice and warm. I use a infra-red therm. and heat the feeder over 100. (I use a heat lamp with a dome), some use hairdryers, some heat mats. I personally keep the feeder dry. So I let it just thaw out near the tub or on top of the tub, then heat it up.
2. I use a long tweezers to and grab the feeder by the mid back skin and bring him horizontally toward the snake, just as it would come if it was alive. Make it go toward it's nose and back from the nose just like a scared mouse or rat would act. Make it act alive. But don't hit or scare the snake. Sometimes holding real still is the best scenario.
3. I try to read my snake to make sure it is hungry, example it is cruising around the hide looking to leave or his head is just inside the hide, strike ready. If it doesn't work the first time, reheat and try again. If it doesn't work that night. Wait 5-7 days and try again. Don't give in and feed live the next day. Monitor your snakes weight and use compassion and common sense. Mine didn't want to eat the first time but I waited a few days and it worked great the next time.