Go with the Magnesium aspartate dihydrate. You did not mention the other Magnesium supplement contents and different magnesium salts can be next to useless.
Remember that there is nothing wrong with dosing higher than I suggested with the magnesium. The only side effect is flushing of the skin, and diarrhea. You will find the sweet spot. When you limbs stop jerking you know you are on the way
You can also purchase Taurine from most vitamine shops. A reputable body building brand that starts with the letters (Mus) and ending in (i) will sell taurine in 75 gram tubs. It is very cheap and is very easy to dose. (Tastes kind of sweet)
Doxylamine Succinate is actually the best of the otc sedating antihistamines, but if you have access to mirtazapine, then this will be very beneficial. (Might need to talk to a doctor about that one though) 7.5mg Mirtazapine should be enought to put you to sleep without any negative problems related to high doses.
If you really cannot get mirtazapine (Avanza), and you are looking for another antihistamine that might do the job, try polaramine (Dexchlorpheniramine maleate). Polaramine comes in two preperations, Instant release and slow release. Ask for the ir version for sleep.
You will find that polaramine (very mild) does not put you out like either mirtazapine or doxylamine succinate, but it is better than nothing. However it does not have most of the nasty side effects associated with the stronger antihistamines.
Other than the above comments, I have nothing else to add.
All the best with the quitting.
Benzos are terrible things when you become dependant.
I am more than happy to answer any more questions you might have. Also if you need support, just drop us a line.
Nab