pull ups for small babies

[ch1134]

I am interested in 'elimination communication' (early potty training) but have left it a bit late. Anyway, ds is 12 months, incredibly wriggly and active, and hates nappy changes. He won't lie down and I have to chase him around the room.
My sister suggested pull ups to make changing easier and I'm willing to try it but can't find any smaller than size 5. He's dinky (size 3 now). Anyone else started pull ups early? Thanks.