Hello, Emilie.
Congratulations on launching your business! I'm here to guide you on what plan to choose for your online clothing boutique.
Choosing a plan depends on how you're going to run your business and your tax obligations.
Self-Employed can prepare the Self-Assessment taxes but there isn't a VAT feature to track your VAT sales and purchases. On the other hand, the Online versions can do both.
The Plus version also has the Stock feature, if you're planning on tracking your clothing stocks.
The full product comparison can be found here: https://quickbooks.intuit.com/uk/pricing/
Though, I would suggest signing up for a trial first before purchasing a plan. On the Pricing page, toggle the Free trial button to on.
After signing up, need to familiarise yourself with QuickBooks Online or set up banking in Self-Employed? Check out these help pages for a guide:
Hoping you'll have a successful business launch. I'd be more than happy to help you out again if you have questions about both programs.