Recommendation for Mobile Service

Hi, I own a mobile service that goes to the customers’ house/ job to install trailer hitches, running boards, roof racks, etc. Currently I bill online via Wave but write down each customer’s name, what parts I need to order, etc in a notebook and check off each thing as it comes in before scheduling on google calendar. Looking for a way to digitize and modernize the process to save time and keep things from falling between the cracks. I don’t need any fancy marketing tools as we’re a well established company and while sure, more sales would be nice right now the focus is just on digitizing our ordering process and being able to keep track of what’s on hand, what’s in transit, etc. Thanks in advance!