Shopify Product Page Customisation

Hi, I’m looking for some help customising our Shopify product pages. Our website is wearthat.co.uk At the moment, customers have to select one size at a time and add each item to the cart individually... (Budget: £250 - £750 GBP, Jobs: HTML, JavaScript, Mobile Development, Shopify, Shopify Development, Shopify Templates, Web Design, Web Development)