Looking for a module to customize order success page and should be mobile responsive too.
Maybe you can share which kind of customization do you want (just to be sure if we're talking about features or design)
You can try the Better Thank You Page by Aheadworks for the purpose.
Plese, visit its product page in our store for more information.
Product page - https://goo.gl/26xqjo
Frontend demo - https://goo.gl/T1QoMi