What you said yourself, only thing that's really visible between 1 and 5 is the flower. And I'm not even sure if it should be counted as knuffel evolution. If someone asked me to describe stage 1 and 5 in short sentences it would be "Boy in black shorts and top" and "Boy in black shorts and t-shirt". Long story short: he hardly changes at all and he's same thing in stage 1 and 5.
You could start with something much simpler: boy only in very short shorts (no bandana or top) and very short hair. Then in next stages add white top, then make it into t-shirt, add print, make something visible with shorts and hair, add small thin bandana, then next stage make it bigger with print etc. You should add bit more elements as well to add more to evolving, but hard for me to suggest something since he's your oc, so not sure what would fit or not. But yeah, bigger shoes, socks, undershirt, purple strands in hair, body parts (for some reason cat ears and tail seem like they'd fit him).