There is NO reason to worry about lactic acidosis. The reason there is a mention of it on the prescribing information is that a related old drug caused it many years ago. But all the studies have shown that the incidence of lactic acidosis among people with metformin is EXACTLY the same as among those NOT taking it.
If you ever go in for a radiology procedure that uses contrast medium they will tell you to stop metformin for a few days before. In an emergency they’ll tell you just not to take any AFTER the procedure for a few days.
I went off my metformin for a few months because I’d developed a little ulcer and it was annoying it. I gained 5 pounds so fast I didn’t know what hit me. I’m back on it and they are coming off. And I’m not even very insulin resistant. The metformin does almost nothing for my blood sugar, but BOY does it help maintain my weight!