DESIGN and optimize email opt-in conversions from my website

My website is www.puppiesdaily.com. I have a sidebar email opt-in form which doesn't get many subscriptions, and a lightbox opt-in form that has about a 1.5% conversion rate for email subscriptions. My site uses Wordpress framework and I use Thrive Leads to create my opt-in forms. My conversion rate is lower than I would like. I need a person or company with experience in DESIGNING catchy and successful opt-in forms, run tests against different opt-in forms, and implement new types of opt-ins on the site (in addition to sidebar or lightbox). My goal is to achieve an opt-in rate of > 3% on the light box, and hopefully around 3% on a new type of opt-in form. The sidebar form may not do as well, but any creativity to increase conversions will be helpful.