Shopify Website Conversion Optimization and Customization

We are looking to optimize the shopify website theme in a way to increase the purchase conversion rate while changing few things. Someone who can look at the competitors and give us best funnel website in the current market. The website should not have any glitches or problems after completion. This will not only be optimizing the funnel but optimizing the main page and the product page. Someone who have advance knowledge of graphic designing, language and optimization of shopify theme, images and to make sure it looks perfectly fine on different apps and devices.