Build an e-commerce website

I currently have a website and domain with heart internet, it works with Wordpress and has been custom built. In the process of changing domain names, the website pages aren't all pointing to the new domain, and it also not very mobile friendly. I am looking to move from heart internet to shopify or have website revamped and made fully ecommerce (whichever is easier, cheaper and faster). Please do come back with siggestions and bids. Need it quite quickly. Thank you