Remember, this is just a game, not everyone wants to get down to the gritty like you are wanting to do for this spell
It sounds like you are wanting to cut out the options that, I feel, are what it is mainly for. Saving yourself from certain situations that arise, such as from hp loss and such. Since those are very hard to talk about in character terms it should be fine to talk about them in player terms and have the character translate, this should be easy and fine really.
In the other sense it sounds like you have no problem with the ones that, I feel, it should not be able to do. Such as, 'whenever king of land X 3000 miles away dies cast prestidigication to make a little skull and crossbones in the air 3' in front of me'. While interesting, I dont like that part of the spell.
So I really like the parts that the character is aware of directly, and could describe to himself, even if he couldnt describe it to others. We all know when we feel ill, or are hurt, or any number of other things where words simply fail us. I would be fine with the player describing, to the best of his ability, what he wants it to trigger on and when that occurs, so long as it is within the bounds of the spell as I describe it to them, let it happen. Even if that means, 'when I have 10% or less or my hp remaining then cast heal on myself'. In player terms this is easy and fast, in character terms it is something like, 'when I feel this bad or worse'.
It is exactly the same, and thereby a good option, since it isnt game breaking. If anything it helps to make the spell easier for what it seems to me that it should be for.