Add a pop-up on our current website to collect email addresses by offering a discount on first purchase

We've got a website with an online store. We would like to create a pop-up screen for people to join our mailing list so that we can start collecting email addresses. We will offer and incentive for them to join the mailing list by offering a discount on their first purchase. The pop-up needs to be mobile responsive and blend in with the current website. I am looking for a Wordpress expert who also knows Woocommerce.
I am also looking for someone to work on our website ongoing. I am looking for someone who I can trust and build a relationship with. Someone who can respond quickly to requests and is very accurate with great attention to detail.