Based on your answers, my personal recommendation for your business is MailChimp.
MailChimp is best for businesses that are either just getting started or are on a seriously shoestring budget. The automation is very basic but it will get the job done.
The most important thing is for you to start building your email list… email marketing is the most profitable channel in your business, offering 40x greater ROI than Facebook or Twitter!
Keep in mind that as your business grows, you'll likely want a solution that can scale with your needs… if you're serious about email marketing, you'll quickly outgrow MailChimp and want a more robust email marketing platform like GetResponse, ConvertKit or Ontraport.