If you used BAQ henna, it is unlikely that you will get back to anything other than strawberry blonde. I have been able to lighten henna maybe 2-3 levels using color remover (mostly useless) and bleach (Wel-lite Oil). Because of the way henna deposits, bleach just isn't able to efficiently lift it. Assuming you can get it back to the same level, it will be difficult to remove the warm tones without seriously trashing your hair (and even then, it's not a guarantee)
You might be better off to commit to a year or so of regular highlighting and gradually transition back to blonde.
Highlights won't look "weird" so long as you don't go platinum streaks in, say, level 5 auburn (and even then, weird is totally subjective.) If you're going for more natural/subtle, I would go with highlights a level or 2 lighter than your hair, and just gradually lighten them.