I'm currently using WordPress for our main site, which is content driven, and linking to a nopCommerce shopping cart on another site as an ecommerce solution. This nopCommerce is a customized solution since we have to provide login and password to access our shopping cart (we only sell medical products to doctors), and they have access to their account and some features like downloadable products section, past orders, re-order, etc. We'd really like to integrate our wordpress content site and add on an ecommerce solution that works with wordpress - unlike nopcommerce which does not (or as I understand would take effort to work with it).
I've read a bit about woocommerce and other options, but was looking for advice on the best ecommerce solution that can be fully customized and offer login, password, and account options, as well as customized automatic notification emails, UPS world ship integration - basically something that a developer can work around and give us the most customized options and integrate with WordPress. Would appreciate any advice as it seems nopcommerce is not the way for us to continue if we want to play our content and ecommerce all on one site.