1045 or any medium carbon steel would be fine. Problem is these can be difficult to machine on a small lathe, at least to get a good finish. Your best approach would be to turn the bearing sizes about 0.001" to 0.002" oversize and then carefully finish them to size with a fine file and emery cloth. It will take several miuntes and you need to creep up on the final size gradually because you need a tolerance of 0.0005" or so.
Take care not to get hung up on a spinning chuck with either the file, the emery or the sleeve of your shirt and only run at 200 or 300 rpm for the filing and polishing.