Newsletter form on mobile

I'm having a mobile version of my (fashion shopping) site built.

My team and I are arguing over whether, when and where the "sign up for our newsletter" prompt should appear.

We're looking to encourage users to sign up without nagging too much.

My team thinks a modal window with 100% width and 100% height opaque background is the best solution. I think it is a horrible idea, as people won't sign up without having visited the site and will close the modal window as soon as they can. in addition, I think it will discourage users from both browsing our site and signing up to our newletter.

My solution is a floating bar perhaps with css of position: fixed; bottom: 0; on the bottom of the page, maybe semi-transperant, which can be closed easily by clicking on close icon. One of my team members has signed it off as annoying.

It is important to note that newsletter recipients get a 10% exclusive coupon to our site which is unique to them, so there's an incentive for them to sign up.

Am I approaching this wrong?