Hello and welcome to the forum. Thanks for your question. This is a good discussion to have with your doctor. Metformin, the immediate release version and Metformin, the extended release version are the exact same medication. The extended release version just doesn't have to be taken as often as it is released over time. The bid or twice a day schedule with the Metformin you currently take will work as well as the once a day extended release version. That's really the main difference.
I think asking to be on Metformin ER is an excellent query for your doctor. To me it should be a mutual decision. Good luck to you.
Question is how well your blood sugar is controlled and whether you have any tummy issues.
One of the major reasons that people may use extended release is that it can reduce tummy upsets, if one experiences that.
However, certainly a good question for your doctor.