Thumb sucking baby advice

My baby has had a pacifier since a month back, but I've been very restrictive with it since I really hoped we wouldn't have to use one. Now I have noticed he will suck his thumb when he doesn't have his pacifier, so every time I see his thumb going in his mouth I give him the pacifier instead, since I've heard it's better to make them use pacifiers if possible. Does anyone have any more advice on how to avoid him turning into a thumb sucker? Baby is eight months old.