My boy kept sucking his fist too, especially his thumb. I can't monitor him every minute so whenever i go back and check on him, will find his mittens wet wet. I scared if he continue to suck, when i remove his mittens he will suck his thumb, then his nails will be short short and fat fat.
Also, I found that sometimes he has a hard time falling asleep deep in the afternoon. So I gave him the pacifier and within 1 minute he fell asleep deeply. I'm like..where has all my carrying gone to...
But I'm trying to limit his time on the pacifier, scared he rely too much on it like what
@snowfern mentioned. Also using the Avent one, seems like he like it. Suck until quite loud.