Customize Salesforce that an IO can have several line items

Hi, in our IO´s (insertion order) at salesforce we already added some custom fields to specify what the client ordered, but we can always add only one product. Similar to a shopping cart ,we need to be able to add more products to the IO that then are summed up at the end. We have roughly 5 different types of products that need to be able to be added, and each product has different additional information, like size, target group, quantity, price single, count, price sum, ... that need to be specified. We would be happy to find someone that supports us on an hourly basis since we have other customizations as well that we need later on, for example to have reportings on product basis. best, Kai