You know, you might wanna think about buying a weanling as your new horse for that very reason. While Bay is still active enough for you to ride, you could be training the young one up the way you'd want him trained. With you being able to work from home and spend more time with him than the average person, plus having the knowledge that you have, you should have an extrordinarily well behaved horse by the time it's ready for him to be broke to ride, whether by you or someone else. Like you say, the trust issue would already be resolved.
It's a thought! It sure would be fun to do all the training on my own (though I'd probably send him out for backing, like you did) but I hadn't thought I'd want to replace Bay with a really green horse.
And really, we're maxed out here... we don't really have room for another till we get our own place.