Gentlemen, welcome to the forums! I'm sorry to hear you're not feeling well and yes, I get that this is a massive existential understatement, but I do mean it. You might find this hard to believe, but I too have struggled my entire life with depression/anxiety along with intermittent thoughts ranging from "I would be better off dead" to "I wish I was dead" to "I'm killing myself right now", so while I would never venture to speculate on the extent of another's pain, we have a lot in common. I too am an Opioid user with the usual accompaniment of poly-substance-tomfoolery. Who knows, we might even become pen-pals or something. I've got a lot of free time this week so try me.
If you would like to talk about how you're feeling, you can always send me a private message, but if you just want the straight-up advice on your drugs, I need more information. While your weight is definitely a factor in determining dosage, it's really quite a small one. What is more important is knowing what your tolerance to and experience with Methadone/Opioids is along with your history with Benzo's. We cannot make an accurate determination without this information.
In the best of circumstances, Methadone and Benzodiazepines tend to be disproportionately problematic. Methadone possesses a major potential for respiratory depression, even relative to other Opioids. If this is your first time with both or you're unfamiliar with Methadone in general, we definitely need to talk about this, because there are many potential pitfalls involved for the uninitiated user.