Using thumb / finger comfort?

Le

We only breast feed

She’s 12 weeks and is chomping on her hand she gets quite upset when she can’t reach her hand to her mouth when in car seat or pram

Debating if now we should introduce a dummy

I only worry she will use that more then feed i worry as currently I’m like right she’s been fed, nappy done she’s Cryin because she’s tired but if she had a dummy would I miss signs?