Please suggest me a Commerce plugin for easy payment.

Hi, everyone, I am planning to build a site to sell social services, so I list all my services paakcages in one page with buy now button below each package, so when my clients click the buy now button, I need a popup shows up which allow him to enter username and then click the pay button to pay with paypal. Does anyone knew any plugin can do this? Thank you very much.

P.S. I am using WordPress.