Is there a reason you are winding one rather than buying one? Especially a torroid, hand-winding those for low frequencies is a horrible job.
This doesn't sound like an application needing isolation, so an autotransformer would be a good plan, smaller for the same power, or lower impedance for the same size. A 1:1 isolating transformer could also be used as an autotransformer here.
What power rating do you need?