Sorry to tell you this, but there is no "stopping" progression without starting treatment. Make sure you are seeing a Myeloma specialist, even if as a second opinion to work with your local oncologist. This is VERY important, Also, going from SMM to full-blown MM in two years is fast, It is usually 5% chance per year.
https://www.patientpower.info/multiple-myeloma/...

Multiple Myeloma: Causes, Symptoms, and Treatment Options

https://www.patientpower.info/multiple-myeloma/overview

I'm also smoldering. Some people claim that antioxidant supplements like turmeric curcumin, astaxanthin, and green tea may be beneficial. When I asked my hem-onc about supplements and foods high in antioxidants, he was not against it and advised me on what things to try. I've been taking the aforementioned supplements for about two weeks now. I'll be posting an update if I see any improvement in my labs.

I was diagnosed with SMM in July, 2012. By August, 2014, the SMM had progressed to the point at which I had to start treatment. I'm not aware to anything I could've done to slow the progression. Certainly I was not advised of any lifestyle changes. Keep in mind that some patients live with SMM for years, even decades before it progresses to MM. Sometimes it never advances to MM.