Is there a guide to copying all data from self employed to online correctly?

Yes, we have an article that will guide you in transferring your data from QuickBooks Self-Employed to QuickBooks Online, Oscar28.

You're right that these two accounts operate differently, as QBSE is a single-entry accounting system, while QBO is a double-entry accounting approach. Since they categorize and track entries in distinct ways, this might be the reason why your personal transactions are impacting the main figures. That said, I would like to know how you migrated your data from one to another.

If you upgraded directly from QBSE and imported your data into QBO using the Bring my data feature, review the categories you selected for the open transactions and invoices. Conversely, if you exported the entries or report and reimported the CSV file in QBO, you'll need to recategorise them because some categories may not display correctly. To ensure you're assigning them to the correct account, consider consulting an accountant for further help.

Refer to this material for step-by-step instructions to ensure everything is in order: Switch from QuickBooks Self-Employed to QuickBooks Online. 

Once you're all set, get started and adjust settings to maximize your experience with the Online version.

Please notify us of any additional assistance you require when migrating data or navigating within QuickBooks. We'll be here to help you.