Maybe I'll stick with what I've got. I'm happy with the fact that it's just a melody instrument and I don't need to worry about the chords. It's just that everyone else seems to start with whistles or recorders and move on.
And I haven't been practising much lately.
All the others are Yes, But... instruments. I never could play a mouth organ, and I can't imagine having to work out which hand to use for which note for an English concertina. I rather liked the bowed psaltery, but I bet they need a lot of tuning. A melodean was suggested, but I wouldn't want something that didn't have all the notes. Etc, etc.
Thanks everyone. Shaky egg may be my best bet. I've got a frog, for when they play the frog tune at Audlem.