Thank you Imogen. Lol its OH who is scared of rats, not stepson
Can you really get a chipmunk? I did suggest sugargliders and stepson was quite keen at first but he googled "do sugar gliders make good pets" and unfortunately the first article he came across said no. So that was that.
Birds we ruled out. Not just for asthma (which may or may not be an issue) but I know a bit too much about bird fanciers lung so am paranoid about that. Although my nana had budgies for years without issue.