I was hoping that you were still on line. As you're not, I will give you an answer and if you need to follow up, you can reply to this question thread once you're at your computer.
In Oregon, possession of meth is a class C felony, punishable by a maximum of 5 years of prison. Like any other criminal defendant, you are going to have two broad choices, to fight the case, all the way to trial and verdict, if necessary, or to get a deal. If you go to trial on the case and get convicted of the felony, prison is inevitable, and your maximum risk would be the 5 years I mentioned.
If you want a deal from the prosecutor, you should be able to avoid an incarceratory offer. However, unless the prosecutor is willing to reduce the charges to a misdmeanor, where you can possibly negotiate to do community service or pay a fine, an offer on the felony is generally going to involve drug treatment or straight probation. Either way, it would be expected that you remain drug free as part of the condition of your continued release.
You would appear to be a good candidate for drug treatment court, which would get you help with your addiction problem and give you the opportunity to learn how to cope without drugs and to get your case dismissed after you completed your court obligation. I understand why you'd be resistant to it, but it's the standard offer for a case like this and possibly the best offer you're going to get as the prosecutor is not likely going to be moved by your desire to stay addicted to illiicit substances, however responsibly you believe you are while on it.
Your best chance of getting a reduction in charges and the ability to avoid probation/treatment and mandatory U/As would be with a lawyer. It may be tough for you to afford one, but given the status quo you wish to maintain, and here I'm talking about your job and being able to care for your mother, you can't afford not to hire one.
Your best course would be to go in on Monday, plead not guilty at your arraignment to keep all of your rights and choices open and ask for a continuance to come back with counsel. You can try to speak to the DA for yourself, but in the first place many prosecutors will refuse to negotiate with an unrepresented defendant, and in the second anything you say to anyone other than your lawyer can be used against you, which means if he is not sympathetic to your plight you will have made admissions to the prosecution that will hamper you and prevent you from fighting the case as successfully, if you can't get the deal you want.