Steel reels can be easier to use for 35mm, but I haven't seen them be much improvement for 120. If you can do it outside of the bag, its a room issue, not a reel issue, so maybe the key would be to replicate the roominess of being outside the bag. Maybe use something, like coat hangers, to puff up the changing bag. Personally, I use a dark closet and have never owned a changing bag.