What’s the best way to track profit for the tax man?

Hi, I’m operating as a sole trader running a very niche small business (golf balls) through eBay at the moment, I have an excel spreadsheet detailing how much each product returns and the profit from each. I’m wondering how you all keep track of profit. The two main reasons are that I want to be able to be net loss before the end of the tax year, so that I don’t have to pay tax until I’ve scaled up a bit, and I want to see how lucrative this business is. I have a wide range of products, some returning over 200% of costs and some at a small loss (necessary to move bulk golf balls)

I suppose I’m hoping that you don’t have to keep track of every product sold and there is a streamlined process that other small businesses use. Id appreciate any advice :)