Suboxone poses a much more lengthly withdrawal than does Tramadol. It would not be wise to begin Suboxone and I hope you haven't... Also, the main reason you don't want to quit Tramadol cold turkey is because of the high risk of seizures... Good luck.
I am a physician who treats chronic pain and i prescribe opiates every day. Alison is correct that tramadol can cause physical dependence. When you say you are addicted to the drug it makes me think you are on large amounts, which would make withdrawl more likely. I taper opiates for a living and decreaseing the dose by 10% per week is nearly 100% safe. This, however is very difficult to do as an outpatient and requires a great deal of self discipline. Some of my patients have told me about a 3-2-1 program of opiate tapering that they (mostly) endorse. Suboxone will work but only if you are taking substantial amounts of tramadol; if you are on small amounts, it could conceivably make your dependence worse. Being on zoloft and large amounts of tramadol introduces another risk too which I won't go into here.
It is not safe to suddenly stop tramadol because it will cause withdrawal effects. A few of the effects are anxiety, nausea, tremor and sweating. You should contact the doctor to help you come up with a proper way to taper the dose to minimize the effects of withdrawal.