Database/spreadsheet required for multi channel inventory

We are a mail order stationery company and currently offer our products for sale across 4 UK sales platforms, including our web site on Shopify.
We are looking for a simple database to be written to hold our data in one place. We are looking for data analysis across the different platforms to include stock levels, inventory, forecasting, profit per platform and inventory reporting. If possible, we would like real time reporting – especially across Amazon – as we sell in three different ways on this site. This database will be worked on daily and will be an important tool for us.
There will be a tidy up required of SKUs and descriptions as these differ across the platforms and need to be uniform.
For someone proficient in databases and spreadsheets this should be a straightforward task. Unfortunately, our knowledge of excel and databases is not the best, so we are looking for an expert! We are keen to move forward with this as soon as possible.
Thanks for reading.