From what I've read, hypothermia, hypoxia, starvation, and dehydration are commonly proposed as they would induce cardiorespiratory death criteria rather than neurological criteria. Starvation would probably be preferred as the reduction in fat makes it feasible to cool faster. Nonetheless, if your condition is not causing literal brain damage over time, I don't think it is rational to consider "suicide" for cryonics purposes. Science is constantly progressing, and if you wait longer you are more likely to make it to a point where your depression is curable and actuarial escape velocity is reached. Furthermore there will tend to be better cryonics later on (a process you can likely impact by promoting cryonics related discourse in the here and now).

In the mean time, do everything you can to a) reduce suicide risk, and b) reduce feelings of depression. Get enough sleep, eat healthy, hang out with people with positive attitudes. Get professional help if you haven't already. Things will get better.