We know from research that using higher dosages of addictive drugs correlates directly with the addictive potential of said drug. Someone who injects 50mg of Methamphetamine will become addicted "faster", if you will than someone taking D-Amphetamine 5mg orally.
Drugs like Amphetamines can be used long-term maintaining their therapeutic benefit. This is only the case if the utmost caution and responsibility are practiced. Only use what it takes to make your symptoms manageable, never more. I'm also a recovering addict who has a stimulant prescription (Dextroamphetamine). I was never a stimulant addict though, so keep that in mind.
1mg Dextroamphetamine is like nothing. It makes me question the validity of your product when you say less than 1 milligram is enough to give you severe insomnia. Most people wouldn't be able to tell with surety that they'd actually taken a drug. For most folks, the threshold is going to be 5mg Dextroamphetamine orally to see subjectively, clinically noticeable effects.
As far as things that can help offset the negative side-effects of Amphetamines, you've got options.
Benzodiazepines
Not at all advised. They work like a charm. They are also highly addictive. They're only "effective" for 6 weeks at most. After the 4 week mark, you will start seeing a noticeable decrease in the efficacy of the Benzodiazepines. I am including this in the thread just because I know it will come up in conversation. I do not suggest using Benzodiazepines.
Herbs
L-Theanine, Valerian, Passionflower are just a few of the commonly-used sedatin/anxiolytic herbs that you can find either at the supermarket or a supplement/vitamin shop. I find Theanine and Passionflower to be very effective for me. As with everything, make sure you're buying something legitimate. I mentioned the supermarket, but Ideally, you're not getting this stuff at the supermarket.
Kava
Kava is a tree/shrub that contains sedative/anxiolytic compounds known as Kavalactones. There are folks who swear by Kava both as a remedy for situations like yours and on its own as a recreational substance. It doesn't seem to have risk for addiction/tolerance. I'm sure tolerance is there in some form, I just have never heard anyone actually describe it.
These are some good starting suggestions. Let me know how you feel about this stuff. We can throw some more suggestions at you if need be.