Miss mini-rower40 snr has now outgrown her single-speed starter bike, and needs something with 20" wheels. I'm concerned by the exposedness of the chain of all such derailleur-fitted bikes, the faff of not being able to change gear when stationary, and how close the jockey wheels are to the ground. Is there something I can get for her, off-the-peg/shelf with either a Sturmey-Archer or Shimano Nexus hub gear?